SEC Info℠  
    Home      Search      My Interests      Help      Sign In      Please Sign In

Energy Focus, Inc./DE – ‘10-Q’ for 6/30/22 – ‘EX-101.DEF’

On:  Thursday, 8/11/22, at 8:02am ET   ·   For:  6/30/22   ·   Accession #:  924168-22-71   ·   File #:  1-36583

Previous ‘10-Q’:  ‘10-Q’ on 5/12/22 for 3/31/22   ·   Next:  ‘10-Q’ on 11/10/22 for 9/30/22   ·   Latest:  ‘10-Q’ on 11/9/23 for 9/30/23   ·   12 References:   

Find Words in Filings emoji
 		  in    Show  and   ↓Hints

  As Of               Filer                 Filing    For·On·As Docs:Size

 8/11/22  Energy Focus, Inc./DE             10-Q        6/30/22   72:7.2M

Quarterly Report   —   Form 10-Q

Filing Table of Contents

Document/Exhibit                   Description                      Pages   Size 

 1: 10-Q        Quarterly Report                                    HTML   1.52M 
 2: EX-10.3     Material Contract                                   HTML     42K 
 3: EX-31.1     Certification -- §302 - SOA'02                      HTML     24K 
 4: EX-32.1     Certification -- §906 - SOA'02                      HTML     23K 
10: R1          Cover Page                                          HTML     75K 
11: R2          Condensed Consolidated Balance Sheets               HTML    131K 
12: R3          Condensed Consolidated Balance Sheets               HTML     41K 
                (Parentheticals)                                                 
13: R4          Condensed Consolidated Statements of Operations     HTML     99K 
14: R5          Condensed Consolidated Statements of Changes in     HTML    100K 
                Stockholders' Equity                                             
15: R6          Condensed Consolidated Statements of Cash Flows     HTML    131K 
16: R7          Nature of Operations                                HTML     24K 
17: R8          Basis of Presentation and Summary of Significant    HTML     90K 
                Accounting Policies                                              
18: R9          Restructuring                                       HTML     42K 
19: R10         Inventories                                         HTML     43K 
20: R11         Property and Equipment                              HTML     37K 
21: R12         Leases                                              HTML    143K 
22: R13         Debt                                                HTML     38K 
23: R14         Income Taxes                                        HTML     27K 
24: R15         Stockholders' Equity                                HTML     84K 
25: R16         Commitments and Contingencies                       HTML     23K 
26: R17         Other Income                                        HTML     26K 
27: R18         Basis of Presentation and Summary of Significant    HTML     69K 
                Accounting Policies (Policies)                                   
28: R19         Basis of Presentation and Summary of Significant    HTML     63K 
                Accounting Policies (Tables)                                     
29: R20         Restructuring (Tables)                              HTML     27K 
30: R21         Inventories (Tables)                                HTML     43K 
31: R22         Property and Equipment (Tables)                     HTML     36K 
32: R23         Leases (Tables)                                     HTML     93K 
33: R24         Stockholders' Equity (Tables)                       HTML     79K 
34: R25         Basis of Presentation and Summary of Significant    HTML     63K 
                Accounting Policies - Certain Risks and                          
                Concentrations (Details)                                         
35: R26         Basis of Presentation and Summary of Significant    HTML     34K 
                Accounting Policies - Disaggregation of Revenue                  
                (Details)                                                        
36: R27         Basis of Presentation and Summary of Significant    HTML     28K 
                Accounting Policies - Geographic information                     
                (Details)                                                        
37: R28         Basis of Presentation and Summary of Significant    HTML     43K 
                Accounting Policies - Reconciliation of Basic and                
                Diluted Loss per Share (Details)                                 
38: R29         Basis of Presentation and Summary of Significant    HTML     32K 
                Accounting Policies - Net Loss per Share (Details)               
39: R30         Basis of Presentation and Summary of Significant    HTML     32K 
                Accounting Policies - Product Warranties (Details)               
40: R31         Basis of Presentation and Summary of Significant    HTML     31K 
                Accounting Policies - Warranty Activity (Details)                
41: R32         Basis of Presentation and Summary of Significant    HTML    102K 
                Accounting Policies - Financial Instruments                      
                (Details)                                                        
42: R33         Restructuring - Narrative (Details)                 HTML     41K 
43: R34         Restructuring - Reconciliation of Restructuring     HTML     26K 
                Liability (Details)                                              
44: R35         Inventories - Inventories, Net (Details)            HTML     29K 
45: R36         Inventories - Reserve Rollforward (Details)         HTML     29K 
46: R37         Inventories - Narrative (Details)                   HTML     27K 
47: R38         Property and Equipment - Schedule of Property and   HTML     67K 
                Equipment (Details)                                              
48: R39         Leases - Narrative (Details)                        HTML     30K 
49: R40         Leases - Components of Lease Cost (Details)         HTML     34K 
50: R41         Leases - Schedule of Supplemental Balance Sheet     HTML     34K 
                Information (Details)                                            
51: R42         Leases - Schedule of Future Maturities of Lease     HTML     38K 
                Liabilities (Details)                                            
52: R43         Leases - Schedule of Supplemental Cash Flow         HTML     27K 
                Information (Details)                                            
53: R44         Debt - Credit Facilities (Details)                  HTML     59K 
54: R45         Debt - Streeterville Notes (Details)                HTML     71K 
55: R46         Debt - PPP Loan (Details)                           HTML     29K 
56: R47         Income Taxes - Narrative (Details)                  HTML     33K 
57: R48         Stockholders' Equity - June 2022 and December 2021  HTML     68K 
                Private Placement (Details)                                      
58: R49         Stockholders' Equity - June 2021 Equity Offering    HTML     38K 
                (Details)                                                        
59: R50         Stockholders' Equity - Preferred Stock (Details)    HTML     62K 
60: R51         Stockholders' Equity - June 2020 Equity Offering    HTML     67K 
                (Details)                                                        
61: R52         Stockholders' Equity - Outstanding Warrants from    HTML     38K 
                the January 2020 Equity Offering (Details)                       
62: R53         Stockholders' Equity - Stock-Based Compensation     HTML     35K 
                (Details)                                                        
63: R54         Stockholders' Equity - Estimates Utilized           HTML     36K 
                (Details)                                                        
64: R55         Stockholders' Equity - Stock Options and a Summary  HTML     63K 
                of Activity (Details)                                            
65: R56         Stockholders' Equity - Restricted Stock Units       HTML     45K 
                (Details)                                                        
66: R57         Commitments and Contingencies (Details)             HTML     22K 
67: R58         Other Income (Details)                              HTML     34K 
70: XML         IDEA XML File -- Filing Summary                      XML    128K 
68: XML         XBRL Instance -- efoi-20220630_htm                   XML   1.79M 
69: EXCEL       IDEA Workbook of Financial Reports                  XLSX    144K 
 6: EX-101.CAL  XBRL Calculations -- efoi-20220630_cal               XML    152K 
 7: EX-101.DEF  XBRL Definitions -- efoi-20220630_def                XML    651K 
 8: EX-101.LAB  XBRL Labels -- efoi-20220630_lab                     XML   1.44M 
 9: EX-101.PRE  XBRL Presentations -- efoi-20220630_pre              XML    920K 
 5: EX-101.SCH  XBRL Schema -- efoi-20220630                         XSD    149K 
71: JSON        XBRL Instance as JSON Data -- MetaLinks              342±   530K 
72: ZIP         XBRL Zipped Folder -- 0000924168-22-000071-xbrl      Zip    386K

‘EX-101.DEF’   —   XBRL Definitions — efoi-20220630_def

This Exhibit is an XBRL XML File.

                                                                                                                                                                                
<?xml version="1.0" encoding="windows-1252"?>
<!-- XBRL Document Created with Wdesk from Workiva -->
<!-- Copyright 2022 Workiva -->
<!-- r:bc022726-fc64-47b0-8950-fcf47c4a9564,g:0cd75fbd-4f74-4291-9aee-0dbef269c22b -->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/CondensedConsolidatedBalanceSheets" xlink:type="simple" xlink:href="efoi-20220630.xsd#CondensedConsolidatedBalanceSheets"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/CondensedConsolidatedBalanceSheets" xlink:type="extended" id="ibb5d0d4996cf45dfa82e9500c8f2b1d1_CondensedConsolidatedBalanceSheets">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_58edfd2f-d749-4d68-a5eb-f3460b436509" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_674e01ea-9871-49b7-808e-6eeb42a03dfc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsCurrentAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_58edfd2f-d749-4d68-a5eb-f3460b436509" xlink:to="loc_us-gaap_AssetsCurrentAbstract_674e01ea-9871-49b7-808e-6eeb42a03dfc" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_f21a85c6-0816-4d92-82b6-75b0ffbd8569" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_674e01ea-9871-49b7-808e-6eeb42a03dfc" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_f21a85c6-0816-4d92-82b6-75b0ffbd8569" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_1c3f7483-3489-4b55-bd65-d0d2f45d0345" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsReceivableNetCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_674e01ea-9871-49b7-808e-6eeb42a03dfc" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_1c3f7483-3489-4b55-bd65-d0d2f45d0345" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_7b78d6ee-c2cf-4e31-bb95-ea36d32a52aa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_674e01ea-9871-49b7-808e-6eeb42a03dfc" xlink:to="loc_us-gaap_InventoryNet_7b78d6ee-c2cf-4e31-bb95-ea36d32a52aa" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositsAssetsCurrent_4f548eab-fd6d-40bb-97ac-fc9203e25260" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DepositsAssetsCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_674e01ea-9871-49b7-808e-6eeb42a03dfc" xlink:to="loc_us-gaap_DepositsAssetsCurrent_4f548eab-fd6d-40bb-97ac-fc9203e25260" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_5cc87f1c-023b-4cc0-af33-3fe5b454c0b6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_674e01ea-9871-49b7-808e-6eeb42a03dfc" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_5cc87f1c-023b-4cc0-af33-3fe5b454c0b6" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_a32ae2b6-fcc7-4f9a-b7dc-7ff73517e038" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_674e01ea-9871-49b7-808e-6eeb42a03dfc" xlink:to="loc_us-gaap_AssetsCurrent_a32ae2b6-fcc7-4f9a-b7dc-7ff73517e038" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_26c57870-886a-487e-9cb4-18fbde4057c5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_58edfd2f-d749-4d68-a5eb-f3460b436509" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_26c57870-886a-487e-9cb4-18fbde4057c5" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_ba506642-fde4-4c86-bc8a-a581ca4e823c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_58edfd2f-d749-4d68-a5eb-f3460b436509" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_ba506642-fde4-4c86-bc8a-a581ca4e823c" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_33e74a55-19a1-445a-aec4-edb903ae57bd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Assets"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_58edfd2f-d749-4d68-a5eb-f3460b436509" xlink:to="loc_us-gaap_Assets_33e74a55-19a1-445a-aec4-edb903ae57bd" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_2e0e5db9-7d99-4dd4-b570-95b60ae26217" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_58edfd2f-d749-4d68-a5eb-f3460b436509" xlink:to="loc_us-gaap_LiabilitiesAbstract_2e0e5db9-7d99-4dd4-b570-95b60ae26217" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_2e0e5db9-7d99-4dd4-b570-95b60ae26217" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_9d9e4deb-a482-4e67-b253-6e1892459edf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsPayableCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:to="loc_us-gaap_AccountsPayableCurrent_9d9e4deb-a482-4e67-b253-6e1892459edf" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_6cb92892-40a1-460f-8736-d77045625bac" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAccruedLiabilitiesCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_6cb92892-40a1-460f-8736-d77045625bac" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedProfessionalFeesCurrent_193b5a38-d24c-4393-92f0-35fe140b3aa1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedProfessionalFeesCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:to="loc_us-gaap_AccruedProfessionalFeesCurrent_193b5a38-d24c-4393-92f0-35fe140b3aa1" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedEmployeeBenefitsCurrent_4e5c03f3-4589-4c42-a6c8-142130dc94bf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedEmployeeBenefitsCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:to="loc_us-gaap_AccruedEmployeeBenefitsCurrent_4e5c03f3-4589-4c42-a6c8-142130dc94bf" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedSalesCommissionCurrent_f7011ad6-21b1-48ac-a20a-348c21809e83" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedSalesCommissionCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:to="loc_us-gaap_AccruedSalesCommissionCurrent_f7011ad6-21b1-48ac-a20a-348c21809e83" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StandardProductWarrantyAccrualCurrent_312097f3-c949-47ab-8a13-d27c4ec7c0fa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StandardProductWarrantyAccrualCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:to="loc_us-gaap_StandardProductWarrantyAccrualCurrent_312097f3-c949-47ab-8a13-d27c4ec7c0fa" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_1ab88b42-e6b9-4bc6-b916-19760d934a9d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_1ab88b42-e6b9-4bc6-b916-19760d934a9d" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_f79b260e-6918-48be-9249-09790979145a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_f79b260e-6918-48be-9249-09790979145a" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityCurrent_bdcf4f09-18e1-4088-9779-590e6de31f2d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilityCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:to="loc_us-gaap_FinanceLeaseLiabilityCurrent_bdcf4f09-18e1-4088-9779-590e6de31f2d" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableCurrent_3c860d76-046c-4b55-bd12-d352a46f473b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NotesPayableCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:to="loc_us-gaap_NotesPayableCurrent_3c860d76-046c-4b55-bd12-d352a46f473b" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LinesOfCreditCurrent_fc449a95-66a0-45da-8af0-319cfc0715ae" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LinesOfCreditCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:to="loc_us-gaap_LinesOfCreditCurrent_fc449a95-66a0-45da-8af0-319cfc0715ae" xlink:type="arc" order="11"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_0b1f79fb-cbad-49cd-8d67-ecf3dcd431bf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:to="loc_us-gaap_LiabilitiesCurrent_0b1f79fb-cbad-49cd-8d67-ecf3dcd431bf" xlink:type="arc" order="12"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_9f7449f6-2118-4e77-bdb4-72b5ef7a6df6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_9f7449f6-2118-4e77-bdb4-72b5ef7a6df6" xlink:type="arc" order="13"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermNotesPayable_3f9d4f35-2f6b-43f5-8aa3-e6c78cc336c3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermNotesPayable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_216b5eab-275c-4f9f-9fac-6d1434ca74c9" xlink:to="loc_us-gaap_LongTermNotesPayable_3f9d4f35-2f6b-43f5-8aa3-e6c78cc336c3" xlink:type="arc" order="14"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_af9bb467-8516-4cf2-a58f-8391d73c5405" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Liabilities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_2e0e5db9-7d99-4dd4-b570-95b60ae26217" xlink:to="loc_us-gaap_Liabilities_af9bb467-8516-4cf2-a58f-8391d73c5405" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_afd9fdff-a272-4995-9b74-4b595fb4e9f9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_58edfd2f-d749-4d68-a5eb-f3460b436509" xlink:to="loc_us-gaap_StockholdersEquityAbstract_afd9fdff-a272-4995-9b74-4b595fb4e9f9" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_5eca72fa-5984-4fe0-8e46-b65bf8cf785c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_afd9fdff-a272-4995-9b74-4b595fb4e9f9" xlink:to="loc_us-gaap_PreferredStockValue_5eca72fa-5984-4fe0-8e46-b65bf8cf785c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_88742857-e9ff-4048-99cf-264980296eef" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_afd9fdff-a272-4995-9b74-4b595fb4e9f9" xlink:to="loc_us-gaap_CommonStockValue_88742857-e9ff-4048-99cf-264980296eef" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_51943af8-c599-44c5-b288-1d45f6d7d666" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_afd9fdff-a272-4995-9b74-4b595fb4e9f9" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_51943af8-c599-44c5-b288-1d45f6d7d666" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_a7a716b7-c85b-436c-8bf3-6472ebf70956" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_afd9fdff-a272-4995-9b74-4b595fb4e9f9" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_a7a716b7-c85b-436c-8bf3-6472ebf70956" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_268763f2-9255-44e1-b2e0-01eaa303c401" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_afd9fdff-a272-4995-9b74-4b595fb4e9f9" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_268763f2-9255-44e1-b2e0-01eaa303c401" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_25a0e399-ba95-41dc-8e88-068e4167ea48" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_afd9fdff-a272-4995-9b74-4b595fb4e9f9" xlink:to="loc_us-gaap_StockholdersEquity_25a0e399-ba95-41dc-8e88-068e4167ea48" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_fb5983e7-cfa2-40d1-a521-fc669af9bb28" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_58edfd2f-d749-4d68-a5eb-f3460b436509" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_fb5983e7-cfa2-40d1-a521-fc669af9bb28" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_014710c7-a76f-4053-abd0-7196dc2b641c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_58edfd2f-d749-4d68-a5eb-f3460b436509" xlink:to="loc_us-gaap_StatementTable_014710c7-a76f-4053-abd0-7196dc2b641c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_1d7a5af3-61ef-4ba8-953f-e63612ebc871" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_014710c7-a76f-4053-abd0-7196dc2b641c" xlink:to="loc_us-gaap_DebtInstrumentAxis_1d7a5af3-61ef-4ba8-953f-e63612ebc871" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_1d7a5af3-61ef-4ba8-953f-e63612ebc871_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_1d7a5af3-61ef-4ba8-953f-e63612ebc871" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_1d7a5af3-61ef-4ba8-953f-e63612ebc871_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_713f7b8d-c562-4415-b273-50bbafe0135e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_1d7a5af3-61ef-4ba8-953f-e63612ebc871" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_713f7b8d-c562-4415-b273-50bbafe0135e" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_A2021StreetervilleNoteMember_428e1311-a442-4d0a-9b2c-79e8524353a3" xlink:href="efoi-20220630.xsd#efoi_A2021StreetervilleNoteMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_713f7b8d-c562-4415-b273-50bbafe0135e" xlink:to="loc_efoi_A2021StreetervilleNoteMember_428e1311-a442-4d0a-9b2c-79e8524353a3" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_A2022StreetervilleNoteMember_29df3f24-c660-4088-9275-90d84267b579" xlink:href="efoi-20220630.xsd#efoi_A2022StreetervilleNoteMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_713f7b8d-c562-4415-b273-50bbafe0135e" xlink:to="loc_efoi_A2022StreetervilleNoteMember_29df3f24-c660-4088-9275-90d84267b579" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_9dfba437-5be9-4f17-8a47-c9d653163095" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_bb160f4f-b87d-4b47-8607-32614323c688" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/CondensedConsolidatedBalanceSheetsParentheticals" xlink:type="simple" xlink:href="efoi-20220630.xsd#CondensedConsolidatedBalanceSheetsParentheticals"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/CondensedConsolidatedBalanceSheetsParentheticals" xlink:type="extended" id="id3d7fd4a3b134773ade0e3bf8080497b_CondensedConsolidatedBalanceSheetsParentheticals">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_3bcc743f-5807-4756-b0e8-68a998da0e76" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_95a303a2-1852-4f33-a7f2-4484e7ea41d3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3bcc743f-5807-4756-b0e8-68a998da0e76" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_95a303a2-1852-4f33-a7f2-4484e7ea41d3" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_241af327-350e-4dbc-bcc6-2b23980f0f20" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3bcc743f-5807-4756-b0e8-68a998da0e76" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_241af327-350e-4dbc-bcc6-2b23980f0f20" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_7ce98374-56c1-4118-b461-abb47a74d6be" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesAuthorized"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3bcc743f-5807-4756-b0e8-68a998da0e76" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_7ce98374-56c1-4118-b461-abb47a74d6be" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_df64814c-3fbb-48f0-91cd-5c18b4756e74" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesIssued"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3bcc743f-5807-4756-b0e8-68a998da0e76" xlink:to="loc_us-gaap_PreferredStockSharesIssued_df64814c-3fbb-48f0-91cd-5c18b4756e74" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_c5c2acf4-c130-4df1-9756-db45d23de4e8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesOutstanding"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3bcc743f-5807-4756-b0e8-68a998da0e76" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_c5c2acf4-c130-4df1-9756-db45d23de4e8" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_45fe10a4-dbe6-421b-8997-b812bee953e4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3bcc743f-5807-4756-b0e8-68a998da0e76" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_45fe10a4-dbe6-421b-8997-b812bee953e4" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_5323ab42-b232-4cd8-b5a3-d0b734490d07" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesAuthorized"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3bcc743f-5807-4756-b0e8-68a998da0e76" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_5323ab42-b232-4cd8-b5a3-d0b734490d07" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_657a7e93-5248-4080-939f-47ed25f5fa64" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesIssued"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3bcc743f-5807-4756-b0e8-68a998da0e76" xlink:to="loc_us-gaap_CommonStockSharesIssued_657a7e93-5248-4080-939f-47ed25f5fa64" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_36cd013c-7cfd-4a17-b3ae-5637e62339d1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesOutstanding"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3bcc743f-5807-4756-b0e8-68a998da0e76" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_36cd013c-7cfd-4a17-b3ae-5637e62339d1" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_016e121c-405d-4824-a314-cc2b730deb7c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_3bcc743f-5807-4756-b0e8-68a998da0e76" xlink:to="loc_us-gaap_StatementTable_016e121c-405d-4824-a314-cc2b730deb7c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_d9d64096-1199-4edf-aa3a-40c0dfebe8b1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_016e121c-405d-4824-a314-cc2b730deb7c" xlink:to="loc_us-gaap_StatementClassOfStockAxis_d9d64096-1199-4edf-aa3a-40c0dfebe8b1" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_d9d64096-1199-4edf-aa3a-40c0dfebe8b1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_d9d64096-1199-4edf-aa3a-40c0dfebe8b1" xlink:to="loc_us-gaap_ClassOfStockDomain_d9d64096-1199-4edf-aa3a-40c0dfebe8b1_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_284541d8-3201-4d2d-bb2c-3a96d92ce3dd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_d9d64096-1199-4edf-aa3a-40c0dfebe8b1" xlink:to="loc_us-gaap_ClassOfStockDomain_284541d8-3201-4d2d-bb2c-3a96d92ce3dd" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_5ddb69a7-902a-477b-b5f6-83f79fd9a4a9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConvertiblePreferredStockMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_284541d8-3201-4d2d-bb2c-3a96d92ce3dd" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_5ddb69a7-902a-477b-b5f6-83f79fd9a4a9" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/CondensedConsolidatedStatementsofChangesinStockholdersEquity" xlink:type="simple" xlink:href="efoi-20220630.xsd#CondensedConsolidatedStatementsofChangesinStockholdersEquity"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/CondensedConsolidatedStatementsofChangesinStockholdersEquity" xlink:type="extended" id="icef6a9f45c8949cebba381fdf1a5ea70_CondensedConsolidatedStatementsofChangesinStockholdersEquity">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1c021190-3f85-4c87-b64f-4916f9692c30" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1c021190-3f85-4c87-b64f-4916f9692c30" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_5fda2254-4f85-44d9-8769-962ac14f442d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesOutstanding"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_SharesOutstanding_5fda2254-4f85-44d9-8769-962ac14f442d" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_2f221806-f48a-49b0-8f65-bff130297e40" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_StockholdersEquity_2f221806-f48a-49b0-8f65-bff130297e40" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_804a9243-5f41-4490-a400-5285948cd2d8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesOutstanding"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_804a9243-5f41-4490-a400-5285948cd2d8" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_b3f8727b-0a74-4764-bd78-101d3eaea5cf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_b3f8727b-0a74-4764-bd78-101d3eaea5cf" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_9c746950-a3bd-4a1d-b262-b5940cfc71dd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_9c746950-a3bd-4a1d-b262-b5940cfc71dd" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_151bdf75-9c15-4cbc-aa1c-a3bb230ae6bc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_151bdf75-9c15-4cbc-aa1c-a3bb230ae6bc" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_e7d315c1-899d-4892-a212-3d24711fe91c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_e7d315c1-899d-4892-a212-3d24711fe91c" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_1c4d2bfb-ce50-438b-8ad5-c86b743f72d1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_1c4d2bfb-ce50-438b-8ad5-c86b743f72d1" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_35c32bbc-b7f2-4d06-acd9-245c815db6a9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_35c32bbc-b7f2-4d06-acd9-245c815db6a9" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_StockIssuedDuringThePeriodSharesWarrantsExercised_aaa9e578-944c-4387-9545-cf0cc0c57afa" xlink:href="efoi-20220630.xsd#efoi_StockIssuedDuringThePeriodSharesWarrantsExercised"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_efoi_StockIssuedDuringThePeriodSharesWarrantsExercised_aaa9e578-944c-4387-9545-cf0cc0c57afa" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_0897bed0-eb88-466e-b621-03b8eb329414" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_0897bed0-eb88-466e-b621-03b8eb329414" xlink:type="arc" order="11"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts_91ee8c90-e390-488e-90cf-652bc55cb65a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts_91ee8c90-e390-488e-90cf-652bc55cb65a" xlink:type="arc" order="12"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_ca493e57-e691-4b50-bde3-9fe224756484" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_ca493e57-e691-4b50-bde3-9fe224756484" xlink:type="arc" order="13"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_9f1719e7-8b2c-4b67-afc7-8c1ef6d0f7f9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_NetIncomeLoss_9f1719e7-8b2c-4b67-afc7-8c1ef6d0f7f9" xlink:type="arc" order="14"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_94cae561-fdce-47c6-865e-0419976ded87" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesOutstanding"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_2ef25d3c-539c-4f7f-9a7d-21a0dc5c6fb0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_2ca1e511-0021-4fb2-a952-e6afa32da881" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesOutstanding"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_9484d08e-14d3-44e9-8df3-b7e488f507b6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_73b8fb3e-952c-43ca-9b89-2b36e4362ba0" xlink:to="loc_us-gaap_StatementTable_9484d08e-14d3-44e9-8df3-b7e488f507b6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_1b2b6f0e-7a3e-478d-98f0-3df9c1dd2ab1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_9484d08e-14d3-44e9-8df3-b7e488f507b6" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_1b2b6f0e-7a3e-478d-98f0-3df9c1dd2ab1" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_1b2b6f0e-7a3e-478d-98f0-3df9c1dd2ab1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_1b2b6f0e-7a3e-478d-98f0-3df9c1dd2ab1" xlink:to="loc_us-gaap_EquityComponentDomain_1b2b6f0e-7a3e-478d-98f0-3df9c1dd2ab1_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_1633b6ae-e977-4bcd-be04-d3d5e1bae33b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_1b2b6f0e-7a3e-478d-98f0-3df9c1dd2ab1" xlink:to="loc_us-gaap_EquityComponentDomain_1633b6ae-e977-4bcd-be04-d3d5e1bae33b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_7c4d3501-9c1c-4685-a4b5-9f8bfc361e34" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_1633b6ae-e977-4bcd-be04-d3d5e1bae33b" xlink:to="loc_us-gaap_PreferredStockMember_7c4d3501-9c1c-4685-a4b5-9f8bfc361e34" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_7e100436-6693-4dea-a387-1ff2bec7f708" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_1633b6ae-e977-4bcd-be04-d3d5e1bae33b" xlink:to="loc_us-gaap_CommonStockMember_7e100436-6693-4dea-a387-1ff2bec7f708" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_cb7ac03f-9403-4d27-ad48-d3a001921748" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_1633b6ae-e977-4bcd-be04-d3d5e1bae33b" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_cb7ac03f-9403-4d27-ad48-d3a001921748" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_a282681e-b145-4a88-9b22-de054b02e81b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_1633b6ae-e977-4bcd-be04-d3d5e1bae33b" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_a282681e-b145-4a88-9b22-de054b02e81b" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_a56f7caa-43b6-4010-a435-d58b8c1558f6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_1633b6ae-e977-4bcd-be04-d3d5e1bae33b" xlink:to="loc_us-gaap_RetainedEarningsMember_a56f7caa-43b6-4010-a435-d58b8c1558f6" xlink:type="arc" order="4"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="simple" xlink:href="efoi-20220630.xsd#CondensedConsolidatedStatementsofCashFlows"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="extended" id="ia0d19718c97343c9bd1fd08c6094169b_CondensedConsolidatedStatementsofCashFlows">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_1a051d74-3c86-40d0-90f8-ab3184cc3999" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfCashFlowsAbstract_f747e497-0f7d-419a-b06e-d139e8215e91" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementOfCashFlowsAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1a051d74-3c86-40d0-90f8-ab3184cc3999" xlink:to="loc_us-gaap_StatementOfCashFlowsAbstract_f747e497-0f7d-419a-b06e-d139e8215e91" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_7050a5e7-9e02-46e2-8e70-ad1b3a85d1df" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementOfCashFlowsAbstract_f747e497-0f7d-419a-b06e-d139e8215e91" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_7050a5e7-9e02-46e2-8e70-ad1b3a85d1df" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_66c79295-19a8-44fa-b163-e0d526fbbf39" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_7050a5e7-9e02-46e2-8e70-ad1b3a85d1df" xlink:to="loc_us-gaap_NetIncomeLoss_66c79295-19a8-44fa-b163-e0d526fbbf39" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_bc5169cf-900e-48a1-9c93-1041bf6eb300" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_7050a5e7-9e02-46e2-8e70-ad1b3a85d1df" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_bc5169cf-900e-48a1-9c93-1041bf6eb300" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncashIncome_2ed29145-3e74-4921-9eba-bf8067d98455" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherNoncashIncome"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_bc5169cf-900e-48a1-9c93-1041bf6eb300" xlink:to="loc_us-gaap_OtherNoncashIncome_2ed29145-3e74-4921-9eba-bf8067d98455" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_GainLossOnForgivenessOfDebt_c44019b3-8581-41bd-afae-f536cd531807" xlink:href="efoi-20220630.xsd#efoi_GainLossOnForgivenessOfDebt"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_bc5169cf-900e-48a1-9c93-1041bf6eb300" xlink:to="loc_efoi_GainLossOnForgivenessOfDebt_c44019b3-8581-41bd-afae-f536cd531807" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_983d216b-6094-4c32-a7df-3b18a3637aa6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Depreciation"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_bc5169cf-900e-48a1-9c93-1041bf6eb300" xlink:to="loc_us-gaap_Depreciation_983d216b-6094-4c32-a7df-3b18a3637aa6" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_2d2a41c3-b8bc-4771-b52b-da5196351de1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensation"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_bc5169cf-900e-48a1-9c93-1041bf6eb300" xlink:to="loc_us-gaap_ShareBasedCompensation_2d2a41c3-b8bc-4771-b52b-da5196351de1" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForDoubtfulAccounts_2c043fc9-19a3-47ad-bba4-df838c397141" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProvisionForDoubtfulAccounts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_bc5169cf-900e-48a1-9c93-1041bf6eb300" xlink:to="loc_us-gaap_ProvisionForDoubtfulAccounts_2c043fc9-19a3-47ad-bba4-df838c397141" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryWriteDown_612345bb-c56b-4490-b5a2-bfc547659f96" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryWriteDown"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_bc5169cf-900e-48a1-9c93-1041bf6eb300" xlink:to="loc_us-gaap_InventoryWriteDown_612345bb-c56b-4490-b5a2-bfc547659f96" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_IncreaseDecreaseInProvisionForWarranties_6a24ae51-b081-4c26-99f3-4858a0f992bb" xlink:href="efoi-20220630.xsd#efoi_IncreaseDecreaseInProvisionForWarranties"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_bc5169cf-900e-48a1-9c93-1041bf6eb300" xlink:to="loc_efoi_IncreaseDecreaseInProvisionForWarranties_6a24ae51-b081-4c26-99f3-4858a0f992bb" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfDebtDiscountPremium_adf6cf59-f4dd-41e2-9686-92a9356b5d7d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AmortizationOfDebtDiscountPremium"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_bc5169cf-900e-48a1-9c93-1041bf6eb300" xlink:to="loc_us-gaap_AmortizationOfDebtDiscountPremium_adf6cf59-f4dd-41e2-9686-92a9356b5d7d" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_fc672481-16a3-4725-bdd1-8f422dc2acf5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_bc5169cf-900e-48a1-9c93-1041bf6eb300" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_fc672481-16a3-4725-bdd1-8f422dc2acf5" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_c6d6e088-06c6-4383-b058-a1c9a22c4ebf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_fc672481-16a3-4725-bdd1-8f422dc2acf5" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_c6d6e088-06c6-4383-b058-a1c9a22c4ebf" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInventories_01d14b2a-5c82-48e5-a770-caf8f29173a8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInInventories"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_fc672481-16a3-4725-bdd1-8f422dc2acf5" xlink:to="loc_us-gaap_IncreaseDecreaseInInventories_01d14b2a-5c82-48e5-a770-caf8f29173a8" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDepositOtherAssets_0999f000-e947-4873-9438-f2e958c17584" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInDepositOtherAssets"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_fc672481-16a3-4725-bdd1-8f422dc2acf5" xlink:to="loc_us-gaap_IncreaseDecreaseInDepositOtherAssets_0999f000-e947-4873-9438-f2e958c17584" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_5784e7e6-5bde-4cef-8ea0-41e987dd77c2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_fc672481-16a3-4725-bdd1-8f422dc2acf5" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_5784e7e6-5bde-4cef-8ea0-41e987dd77c2" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_7bf68042-093a-43de-8048-2b958a729f67" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_fc672481-16a3-4725-bdd1-8f422dc2acf5" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_7bf68042-093a-43de-8048-2b958a729f67" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_9d00de0c-7ee2-415e-9c26-20b7a628af0c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_fc672481-16a3-4725-bdd1-8f422dc2acf5" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_9d00de0c-7ee2-415e-9c26-20b7a628af0c" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredRevenue_9a1d8916-5145-43a4-b11b-cc9f15e7dc25" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInDeferredRevenue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_fc672481-16a3-4725-bdd1-8f422dc2acf5" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredRevenue_9a1d8916-5145-43a4-b11b-cc9f15e7dc25" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivities_5dd348a4-2bb0-420b-93e8-70dd6b29b9ba" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_fc672481-16a3-4725-bdd1-8f422dc2acf5" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivities_5dd348a4-2bb0-420b-93e8-70dd6b29b9ba" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_0c8670be-5e9a-4280-99a6-7482be94e1cb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_7050a5e7-9e02-46e2-8e70-ad1b3a85d1df" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_0c8670be-5e9a-4280-99a6-7482be94e1cb" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_37ff5651-4762-4ef5-b85e-60a8f0c71fa2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementOfCashFlowsAbstract_f747e497-0f7d-419a-b06e-d139e8215e91" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_37ff5651-4762-4ef5-b85e-60a8f0c71fa2" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_fd6f30df-269e-483d-a969-1cad2e99f647" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_37ff5651-4762-4ef5-b85e-60a8f0c71fa2" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_fd6f30df-269e-483d-a969-1cad2e99f647" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_88b312b2-725c-4e84-816b-54b812acd647" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_37ff5651-4762-4ef5-b85e-60a8f0c71fa2" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_88b312b2-725c-4e84-816b-54b812acd647" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_007d79a9-d313-421b-8c22-69d78b417c62" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementOfCashFlowsAbstract_f747e497-0f7d-419a-b06e-d139e8215e91" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_007d79a9-d313-421b-8c22-69d78b417c62" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ProceedsFromPaymentsForIssuanceOfCommonStockAndWarrants_f4348b25-68ba-4735-bbff-ba891b3095a7" xlink:href="efoi-20220630.xsd#efoi_ProceedsFromPaymentsForIssuanceOfCommonStockAndWarrants"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_007d79a9-d313-421b-8c22-69d78b417c62" xlink:to="loc_efoi_ProceedsFromPaymentsForIssuanceOfCommonStockAndWarrants_f4348b25-68ba-4735-bbff-ba891b3095a7" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromWarrantExercises_d0be3a15-5580-4a48-8f86-2c14f6c5bdc6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromWarrantExercises"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_007d79a9-d313-421b-8c22-69d78b417c62" xlink:to="loc_us-gaap_ProceedsFromWarrantExercises_d0be3a15-5580-4a48-8f86-2c14f6c5bdc6" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_d04f99ec-bd40-404f-ac1d-db75ff870b45" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_007d79a9-d313-421b-8c22-69d78b417c62" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_d04f99ec-bd40-404f-ac1d-db75ff870b45" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeasePrincipalPayments_1eed685c-35d9-4b84-adb7-44b12b73a5f3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeasePrincipalPayments"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_007d79a9-d313-421b-8c22-69d78b417c62" xlink:to="loc_us-gaap_FinanceLeasePrincipalPayments_1eed685c-35d9-4b84-adb7-44b12b73a5f3" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ProceedsFromStockOptionsExercisedAndEmployeeStockPurchasePlans_e751c93a-47d0-4467-a45e-1876083eb2ca" xlink:href="efoi-20220630.xsd#efoi_ProceedsFromStockOptionsExercisedAndEmployeeStockPurchasePlans"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_007d79a9-d313-421b-8c22-69d78b417c62" xlink:to="loc_efoi_ProceedsFromStockOptionsExercisedAndEmployeeStockPurchasePlans_e751c93a-47d0-4467-a45e-1876083eb2ca" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_95583b93-6de5-4617-adee-1a062200419d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_007d79a9-d313-421b-8c22-69d78b417c62" xlink:to="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_95583b93-6de5-4617-adee-1a062200419d" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromNotesPayable_b064c57a-0970-4e1b-917e-c2d783c6fe57" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromNotesPayable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_007d79a9-d313-421b-8c22-69d78b417c62" xlink:to="loc_us-gaap_ProceedsFromNotesPayable_b064c57a-0970-4e1b-917e-c2d783c6fe57" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfNotesPayable_1f41e453-b3c3-433c-8f20-3c00f71600a0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RepaymentsOfNotesPayable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_007d79a9-d313-421b-8c22-69d78b417c62" xlink:to="loc_us-gaap_RepaymentsOfNotesPayable_1f41e453-b3c3-433c-8f20-3c00f71600a0" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfFinancingCosts_3ba9a9fb-8283-43ac-b015-f5d00c397339" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsOfFinancingCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_007d79a9-d313-421b-8c22-69d78b417c62" xlink:to="loc_us-gaap_PaymentsOfFinancingCosts_3ba9a9fb-8283-43ac-b015-f5d00c397339" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromRepaymentsOfLinesOfCredit_12083a94-c29d-4027-b6ca-393cfe8f60f7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromRepaymentsOfLinesOfCredit"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_007d79a9-d313-421b-8c22-69d78b417c62" xlink:to="loc_us-gaap_ProceedsFromRepaymentsOfLinesOfCredit_12083a94-c29d-4027-b6ca-393cfe8f60f7" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_9c63a2c1-2e4f-4f9c-817a-c05fa1cf59c4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_007d79a9-d313-421b-8c22-69d78b417c62" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_9c63a2c1-2e4f-4f9c-817a-c05fa1cf59c4" xlink:type="arc" order="11"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_e18d3352-fd14-41c1-898d-fd90e2b1a473" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementOfCashFlowsAbstract_f747e497-0f7d-419a-b06e-d139e8215e91" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_e18d3352-fd14-41c1-898d-fd90e2b1a473" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_d3bb2523-dafa-4e60-ad9d-7f13a7a4db24" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementOfCashFlowsAbstract_f747e497-0f7d-419a-b06e-d139e8215e91" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_d3bb2523-dafa-4e60-ad9d-7f13a7a4db24" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_dff1ec0e-6983-492c-86e2-480d2b6eed43" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAbstract_fab56c31-43dd-4f1a-a04e-7ef21c7ce489" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAndCashEquivalentsAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementOfCashFlowsAbstract_f747e497-0f7d-419a-b06e-d139e8215e91" xlink:to="loc_us-gaap_CashAndCashEquivalentsAbstract_fab56c31-43dd-4f1a-a04e-7ef21c7ce489" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_14ecf81a-b5a7-4ea6-ba1e-4aa0778c7585" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsAbstract_fab56c31-43dd-4f1a-a04e-7ef21c7ce489" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_14ecf81a-b5a7-4ea6-ba1e-4aa0778c7585" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCash_b3d0e68c-7e6a-48d6-9be6-bb4aa10ae92d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedCash"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsAbstract_fab56c31-43dd-4f1a-a04e-7ef21c7ce489" xlink:to="loc_us-gaap_RestrictedCash_b3d0e68c-7e6a-48d6-9be6-bb4aa10ae92d" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_df9fb165-9991-4a3c-8f72-ef9f50651970" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_3e76f476-204f-40de-9faf-2983dd17e62d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_1a051d74-3c86-40d0-90f8-ab3184cc3999" xlink:to="loc_us-gaap_StatementTable_3e76f476-204f-40de-9faf-2983dd17e62d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_ee73a754-0e49-4287-a9f5-90644bf94e65" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_3e76f476-204f-40de-9faf-2983dd17e62d" xlink:to="loc_us-gaap_DebtInstrumentAxis_ee73a754-0e49-4287-a9f5-90644bf94e65" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_ee73a754-0e49-4287-a9f5-90644bf94e65_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_ee73a754-0e49-4287-a9f5-90644bf94e65" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_ee73a754-0e49-4287-a9f5-90644bf94e65_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_d88c1eef-84b0-4f9e-8fab-9d8ea4e136cf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_ee73a754-0e49-4287-a9f5-90644bf94e65" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_d88c1eef-84b0-4f9e-8fab-9d8ea4e136cf" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_A2021StreetervilleNoteMember_acb6ddcd-e60f-481a-895e-6477798018f1" xlink:href="efoi-20220630.xsd#efoi_A2021StreetervilleNoteMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d88c1eef-84b0-4f9e-8fab-9d8ea4e136cf" xlink:to="loc_efoi_A2021StreetervilleNoteMember_acb6ddcd-e60f-481a-895e-6477798018f1" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_A2022StreetervilleNoteMember_dd71b0e6-51bf-4bc8-b35a-0965b2f3342a" xlink:href="efoi-20220630.xsd#efoi_A2022StreetervilleNoteMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d88c1eef-84b0-4f9e-8fab-9d8ea4e136cf" xlink:to="loc_efoi_A2022StreetervilleNoteMember_dd71b0e6-51bf-4bc8-b35a-0965b2f3342a" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesCertainRisksandConcentrationsDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesCertainRisksandConcentrationsDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesCertainRisksandConcentrationsDetails" xlink:type="extended" id="i174122eb77c24869b95390d3d43f0391_BasisofPresentationandSummaryofSignificantAccountingPoliciesCertainRisksandConcentrationsDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_1b0893a1-cfd9-477a-8541-8c38cdf9139f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_fda63c51-5905-4201-b264-214bda9e9cc2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskPercentage1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_1b0893a1-cfd9-477a-8541-8c38cdf9139f" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_fda63c51-5905-4201-b264-214bda9e9cc2" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_0dcf7d71-69a9-46ae-879e-77184beeef6c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_1b0893a1-cfd9-477a-8541-8c38cdf9139f" xlink:to="loc_us-gaap_ConcentrationRiskTable_0dcf7d71-69a9-46ae-879e-77184beeef6c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_4fc91e3b-243e-4aa1-8e64-2a2d85b52cf9" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MajorCustomersAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_0dcf7d71-69a9-46ae-879e-77184beeef6c" xlink:to="loc_srt_MajorCustomersAxis_4fc91e3b-243e-4aa1-8e64-2a2d85b52cf9" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_4fc91e3b-243e-4aa1-8e64-2a2d85b52cf9_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_NameOfMajorCustomerDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_4fc91e3b-243e-4aa1-8e64-2a2d85b52cf9" xlink:to="loc_srt_NameOfMajorCustomerDomain_4fc91e3b-243e-4aa1-8e64-2a2d85b52cf9_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_30d5efc6-7115-4bef-9360-25a1e5b03369" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_NameOfMajorCustomerDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_4fc91e3b-243e-4aa1-8e64-2a2d85b52cf9" xlink:to="loc_srt_NameOfMajorCustomerDomain_30d5efc6-7115-4bef-9360-25a1e5b03369" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_DistributorToTheU.S.NavyMember_6579b44b-3c55-47cb-8988-67d8d8244e7a" xlink:href="efoi-20220630.xsd#efoi_DistributorToTheU.S.NavyMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_30d5efc6-7115-4bef-9360-25a1e5b03369" xlink:to="loc_efoi_DistributorToTheU.S.NavyMember_6579b44b-3c55-47cb-8988-67d8d8244e7a" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ShipbuilderForUSNavyMember_a8ab43ac-ed17-44a4-acd1-134a427622ff" xlink:href="efoi-20220630.xsd#efoi_ShipbuilderForUSNavyMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_30d5efc6-7115-4bef-9360-25a1e5b03369" xlink:to="loc_efoi_ShipbuilderForUSNavyMember_a8ab43ac-ed17-44a4-acd1-134a427622ff" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_CommercialBuildingSystemsProviderMember_e848e1ea-97b5-4bc7-818d-45c35464fadd" xlink:href="efoi-20220630.xsd#efoi_CommercialBuildingSystemsProviderMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_30d5efc6-7115-4bef-9360-25a1e5b03369" xlink:to="loc_efoi_CommercialBuildingSystemsProviderMember_e848e1ea-97b5-4bc7-818d-45c35464fadd" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_DistributorToTheUSNavyCombinedWithSalesToShipbuildersMember_10c9893f-792e-47a7-84cc-937281d28adb" xlink:href="efoi-20220630.xsd#efoi_DistributorToTheUSNavyCombinedWithSalesToShipbuildersMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_30d5efc6-7115-4bef-9360-25a1e5b03369" xlink:to="loc_efoi_DistributorToTheUSNavyCombinedWithSalesToShipbuildersMember_10c9893f-792e-47a7-84cc-937281d28adb" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_RegionalCommercialLightingRetrofitCompanyMember_51d63695-eca3-439c-a981-6d0e192a44e0" xlink:href="efoi-20220630.xsd#efoi_RegionalCommercialLightingRetrofitCompanyMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_30d5efc6-7115-4bef-9360-25a1e5b03369" xlink:to="loc_efoi_RegionalCommercialLightingRetrofitCompanyMember_51d63695-eca3-439c-a981-6d0e192a44e0" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_DistributorToTheUSDepartmentOfDefenseMember_1e65eaaa-4372-49ed-a7d2-60b85352e651" xlink:href="efoi-20220630.xsd#efoi_DistributorToTheUSDepartmentOfDefenseMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_30d5efc6-7115-4bef-9360-25a1e5b03369" xlink:to="loc_efoi_DistributorToTheUSDepartmentOfDefenseMember_1e65eaaa-4372-49ed-a7d2-60b85352e651" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_CommercialBuildingSystemsProviderOneMember_4ca750a2-c691-4731-ae2e-0be08821c1b7" xlink:href="efoi-20220630.xsd#efoi_CommercialBuildingSystemsProviderOneMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_30d5efc6-7115-4bef-9360-25a1e5b03369" xlink:to="loc_efoi_CommercialBuildingSystemsProviderOneMember_4ca750a2-c691-4731-ae2e-0be08821c1b7" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_CommercialBuildingSystemsProviderTwoMember_b9b33b66-17e3-4d20-83f5-91dd44c21381" xlink:href="efoi-20220630.xsd#efoi_CommercialBuildingSystemsProviderTwoMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_30d5efc6-7115-4bef-9360-25a1e5b03369" xlink:to="loc_efoi_CommercialBuildingSystemsProviderTwoMember_b9b33b66-17e3-4d20-83f5-91dd44c21381" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_48f8aaad-a1df-4c86-a851-c74b1944fef6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_0dcf7d71-69a9-46ae-879e-77184beeef6c" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_48f8aaad-a1df-4c86-a851-c74b1944fef6" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_48f8aaad-a1df-4c86-a851-c74b1944fef6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_48f8aaad-a1df-4c86-a851-c74b1944fef6" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_48f8aaad-a1df-4c86-a851-c74b1944fef6_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6972a201-ce7c-40ca-9520-a88d1a9fc73e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_48f8aaad-a1df-4c86-a851-c74b1944fef6" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6972a201-ce7c-40ca-9520-a88d1a9fc73e" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_dd3d3755-0fff-4f4a-8c17-76488d56e50a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SalesRevenueNetMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6972a201-ce7c-40ca-9520-a88d1a9fc73e" xlink:to="loc_us-gaap_SalesRevenueNetMember_dd3d3755-0fff-4f4a-8c17-76488d56e50a" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_da49b051-d52c-4ca7-bdbc-da8c9a461c8d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsReceivableMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6972a201-ce7c-40ca-9520-a88d1a9fc73e" xlink:to="loc_us-gaap_AccountsReceivableMember_da49b051-d52c-4ca7-bdbc-da8c9a461c8d" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_TotalExpendituresMember_d267c300-3109-4047-90a0-3f1691fa1eed" xlink:href="efoi-20220630.xsd#efoi_TotalExpendituresMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6972a201-ce7c-40ca-9520-a88d1a9fc73e" xlink:to="loc_efoi_TotalExpendituresMember_d267c300-3109-4047-90a0-3f1691fa1eed" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableMember_0167a55c-f2ec-4d72-8162-68dfb20fa8d2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsPayableMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6972a201-ce7c-40ca-9520-a88d1a9fc73e" xlink:to="loc_us-gaap_AccountsPayableMember_0167a55c-f2ec-4d72-8162-68dfb20fa8d2" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_150c615c-2c3f-48ee-8ed1-6b38bb6b0279" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_0dcf7d71-69a9-46ae-879e-77184beeef6c" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_150c615c-2c3f-48ee-8ed1-6b38bb6b0279" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_150c615c-2c3f-48ee-8ed1-6b38bb6b0279_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_150c615c-2c3f-48ee-8ed1-6b38bb6b0279" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_150c615c-2c3f-48ee-8ed1-6b38bb6b0279_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_e0770e3f-47c5-42d4-bdc4-2ec45f8819fc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_150c615c-2c3f-48ee-8ed1-6b38bb6b0279" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_e0770e3f-47c5-42d4-bdc4-2ec45f8819fc" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_56e89335-4976-44e2-a9b9-cd253972914d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CustomerConcentrationRiskMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_e0770e3f-47c5-42d4-bdc4-2ec45f8819fc" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_56e89335-4976-44e2-a9b9-cd253972914d" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplierConcentrationRiskMember_9404d34d-0cf7-4555-8d6c-dd5f112c4678" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SupplierConcentrationRiskMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_e0770e3f-47c5-42d4-bdc4-2ec45f8819fc" xlink:to="loc_us-gaap_SupplierConcentrationRiskMember_9404d34d-0cf7-4555-8d6c-dd5f112c4678" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_dd9073f1-0877-4961-9c5e-d2d20f28219f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_0dcf7d71-69a9-46ae-879e-77184beeef6c" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_dd9073f1-0877-4961-9c5e-d2d20f28219f" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_dd9073f1-0877-4961-9c5e-d2d20f28219f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_dd9073f1-0877-4961-9c5e-d2d20f28219f" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_dd9073f1-0877-4961-9c5e-d2d20f28219f_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_500f843a-85e4-44a8-9e29-5d86a41c928a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_dd9073f1-0877-4961-9c5e-d2d20f28219f" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_500f843a-85e4-44a8-9e29-5d86a41c928a" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_OffshoreSupplierMember_6117fdf1-827f-44ee-ac2a-5444b11d54f8" xlink:href="efoi-20220630.xsd#efoi_OffshoreSupplierMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_500f843a-85e4-44a8-9e29-5d86a41c928a" xlink:to="loc_efoi_OffshoreSupplierMember_6117fdf1-827f-44ee-ac2a-5444b11d54f8" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_OffshoreSupplierOneMember_46a81bd4-9f5e-449a-bd31-4498b08120dc" xlink:href="efoi-20220630.xsd#efoi_OffshoreSupplierOneMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_500f843a-85e4-44a8-9e29-5d86a41c928a" xlink:to="loc_efoi_OffshoreSupplierOneMember_46a81bd4-9f5e-449a-bd31-4498b08120dc" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_OffshoreSupplierTwoMember_3eeb03cc-213d-4cbb-a84b-1dbe38206f3a" xlink:href="efoi-20220630.xsd#efoi_OffshoreSupplierTwoMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_500f843a-85e4-44a8-9e29-5d86a41c928a" xlink:to="loc_efoi_OffshoreSupplierTwoMember_3eeb03cc-213d-4cbb-a84b-1dbe38206f3a" xlink:type="arc" order="2"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesDisaggregationofRevenueDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesDisaggregationofRevenueDetails" xlink:type="extended" id="ic87ac2c601e54d60ab071d7515a93789_BasisofPresentationandSummaryofSignificantAccountingPoliciesDisaggregationofRevenueDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_1a505a2b-d0cf-4901-a795-8534065dc415" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_32bac0a8-94ff-4ad9-9b08-fc23b152eab7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Revenues"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_1a505a2b-d0cf-4901-a795-8534065dc415" xlink:to="loc_us-gaap_Revenues_32bac0a8-94ff-4ad9-9b08-fc23b152eab7" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_b055596d-cc12-4457-b572-ba14c6b91149" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_1a505a2b-d0cf-4901-a795-8534065dc415" xlink:to="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_b055596d-cc12-4457-b572-ba14c6b91149" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_ac24b024-0db3-4faf-aac8-37772e063076" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_b055596d-cc12-4457-b572-ba14c6b91149" xlink:to="loc_srt_ProductOrServiceAxis_ac24b024-0db3-4faf-aac8-37772e063076" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_ac24b024-0db3-4faf-aac8-37772e063076_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_ac24b024-0db3-4faf-aac8-37772e063076" xlink:to="loc_srt_ProductsAndServicesDomain_ac24b024-0db3-4faf-aac8-37772e063076_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_a7936bce-5b78-47bd-b3cf-0a22e83a6cce" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_ac24b024-0db3-4faf-aac8-37772e063076" xlink:to="loc_srt_ProductsAndServicesDomain_a7936bce-5b78-47bd-b3cf-0a22e83a6cce" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_CommercialProductsMember_049c8965-f68b-4f74-a475-85873c07377c" xlink:href="efoi-20220630.xsd#efoi_CommercialProductsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_a7936bce-5b78-47bd-b3cf-0a22e83a6cce" xlink:to="loc_efoi_CommercialProductsMember_049c8965-f68b-4f74-a475-85873c07377c" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_MMMProductsMember_d488542c-2080-4dd7-87a2-2f2a141bd640" xlink:href="efoi-20220630.xsd#efoi_MMMProductsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_a7936bce-5b78-47bd-b3cf-0a22e83a6cce" xlink:to="loc_efoi_MMMProductsMember_d488542c-2080-4dd7-87a2-2f2a141bd640" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesGeographicinformationDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesGeographicinformationDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesGeographicinformationDetails" xlink:type="extended" id="i49d7ee2c16af42b2a708bdef75414778_BasisofPresentationandSummaryofSignificantAccountingPoliciesGeographicinformationDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_ec21a981-5c11-4e51-9915-f20a2d346f57" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_66d9d898-57b2-4269-8486-ada51a00c3e1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskPercentage1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_ec21a981-5c11-4e51-9915-f20a2d346f57" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_66d9d898-57b2-4269-8486-ada51a00c3e1" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_24061e82-ee4e-4f4b-88f5-b5f865ecc51f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_ec21a981-5c11-4e51-9915-f20a2d346f57" xlink:to="loc_us-gaap_ConcentrationRiskTable_24061e82-ee4e-4f4b-88f5-b5f865ecc51f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_6c27f3ef-bba8-4fea-b24d-f649da693d4c" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_StatementGeographicalAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_24061e82-ee4e-4f4b-88f5-b5f865ecc51f" xlink:to="loc_srt_StatementGeographicalAxis_6c27f3ef-bba8-4fea-b24d-f649da693d4c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_6c27f3ef-bba8-4fea-b24d-f649da693d4c_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_SegmentGeographicalDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_6c27f3ef-bba8-4fea-b24d-f649da693d4c" xlink:to="loc_srt_SegmentGeographicalDomain_6c27f3ef-bba8-4fea-b24d-f649da693d4c_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_a8cf312d-798b-47d9-a16c-9919982af100" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_SegmentGeographicalDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_6c27f3ef-bba8-4fea-b24d-f649da693d4c" xlink:to="loc_srt_SegmentGeographicalDomain_a8cf312d-798b-47d9-a16c-9919982af100" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonUsMember_611ba036-1017-48af-8a5f-204a7e3780fe" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NonUsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_a8cf312d-798b-47d9-a16c-9919982af100" xlink:to="loc_us-gaap_NonUsMember_611ba036-1017-48af-8a5f-204a7e3780fe" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_f743e1db-c284-4799-a9a9-a942b914f3ea" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_24061e82-ee4e-4f4b-88f5-b5f865ecc51f" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_f743e1db-c284-4799-a9a9-a942b914f3ea" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_f743e1db-c284-4799-a9a9-a942b914f3ea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_f743e1db-c284-4799-a9a9-a942b914f3ea" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_f743e1db-c284-4799-a9a9-a942b914f3ea_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_fd061d39-74a1-4c3e-89cd-e9675146505a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_f743e1db-c284-4799-a9a9-a942b914f3ea" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_fd061d39-74a1-4c3e-89cd-e9675146505a" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_98a03b68-dacc-4753-9473-2cc7b5b7eab9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SalesRevenueNetMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_fd061d39-74a1-4c3e-89cd-e9675146505a" xlink:to="loc_us-gaap_SalesRevenueNetMember_98a03b68-dacc-4753-9473-2cc7b5b7eab9" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_40cefef0-c048-4357-80ee-75941a90b399" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_24061e82-ee4e-4f4b-88f5-b5f865ecc51f" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_40cefef0-c048-4357-80ee-75941a90b399" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_40cefef0-c048-4357-80ee-75941a90b399_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_40cefef0-c048-4357-80ee-75941a90b399" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_40cefef0-c048-4357-80ee-75941a90b399_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_bb2e8c6e-71b6-4924-b333-8ff15d7da221" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_40cefef0-c048-4357-80ee-75941a90b399" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_bb2e8c6e-71b6-4924-b333-8ff15d7da221" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicConcentrationRiskMember_505ecfb4-bc93-4740-9197-6a901b18eccd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GeographicConcentrationRiskMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_bb2e8c6e-71b6-4924-b333-8ff15d7da221" xlink:to="loc_us-gaap_GeographicConcentrationRiskMember_505ecfb4-bc93-4740-9197-6a901b18eccd" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesNetLossperShareDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesNetLossperShareDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesNetLossperShareDetails" xlink:type="extended" id="ifb99e314bda04de8bb3d7381e227430b_BasisofPresentationandSummaryofSignificantAccountingPoliciesNetLossperShareDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentEffectsOnEarningsPerShareLineItems_a68c2c0d-fe7d-4524-a17f-e58a76fdca2b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ImpairmentEffectsOnEarningsPerShareLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_5b3fa013-4729-4a5f-a272-4a51830eed53" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairmentEffectsOnEarningsPerShareLineItems_a68c2c0d-fe7d-4524-a17f-e58a76fdca2b" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_5b3fa013-4729-4a5f-a272-4a51830eed53" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentEffectsOnEarningsPerShareTable_91470bdb-aa82-45c5-86cb-1cad2dff3fae" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ImpairmentEffectsOnEarningsPerShareTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ImpairmentEffectsOnEarningsPerShareLineItems_a68c2c0d-fe7d-4524-a17f-e58a76fdca2b" xlink:to="loc_us-gaap_ImpairmentEffectsOnEarningsPerShareTable_91470bdb-aa82-45c5-86cb-1cad2dff3fae" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_d5c73a44-1973-44c7-a9c0-1e5e2f325f0d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ImpairmentEffectsOnEarningsPerShareTable_91470bdb-aa82-45c5-86cb-1cad2dff3fae" xlink:to="loc_us-gaap_AwardTypeAxis_d5c73a44-1973-44c7-a9c0-1e5e2f325f0d" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d5c73a44-1973-44c7-a9c0-1e5e2f325f0d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_d5c73a44-1973-44c7-a9c0-1e5e2f325f0d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d5c73a44-1973-44c7-a9c0-1e5e2f325f0d_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_64afbf88-1cd6-4cee-9c56-0521164da1cc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_d5c73a44-1973-44c7-a9c0-1e5e2f325f0d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_64afbf88-1cd6-4cee-9c56-0521164da1cc" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_0d3440f1-d05c-4919-b836-c50f5fe42b59" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WarrantMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_64afbf88-1cd6-4cee-9c56-0521164da1cc" xlink:to="loc_us-gaap_WarrantMember_0d3440f1-d05c-4919-b836-c50f5fe42b59" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_f4a2f192-27b8-4448-a8e2-a2b615a0fa4e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConvertiblePreferredStockMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_64afbf88-1cd6-4cee-9c56-0521164da1cc" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_f4a2f192-27b8-4448-a8e2-a2b615a0fa4e" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockOptionMember_31714b3a-5139-4f4b-88f0-a130bc1840ec" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockOptionMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_64afbf88-1cd6-4cee-9c56-0521164da1cc" xlink:to="loc_us-gaap_StockOptionMember_31714b3a-5139-4f4b-88f0-a130bc1840ec" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_5cbbc194-575e-4920-89ad-e9992e1a1b50" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_64afbf88-1cd6-4cee-9c56-0521164da1cc" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_5cbbc194-575e-4920-89ad-e9992e1a1b50" xlink:type="arc" order="3"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesProductWarrantiesDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesProductWarrantiesDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesProductWarrantiesDetails" xlink:type="extended" id="i660099d237d640e1a56ef48e36fc5643_BasisofPresentationandSummaryofSignificantAccountingPoliciesProductWarrantiesDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductWarrantyLiabilityLineItems_19333f56-a74e-4b02-8562-8bdd8a145e52" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProductWarrantyLiabilityLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_StandardProductWarrantyNumberofYears_2f6d3ab3-b726-42a6-8b73-9213114ba6a0" xlink:href="efoi-20220630.xsd#efoi_StandardProductWarrantyNumberofYears"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductWarrantyLiabilityLineItems_19333f56-a74e-4b02-8562-8bdd8a145e52" xlink:to="loc_efoi_StandardProductWarrantyNumberofYears_2f6d3ab3-b726-42a6-8b73-9213114ba6a0" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductWarrantyLiabilityTable_c715881a-ecd2-4903-9726-f4dff315931c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProductWarrantyLiabilityTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ProductWarrantyLiabilityLineItems_19333f56-a74e-4b02-8562-8bdd8a145e52" xlink:to="loc_us-gaap_ProductWarrantyLiabilityTable_c715881a-ecd2-4903-9726-f4dff315931c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_7a11c91d-b241-4830-b769-b978e71d9044" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ProductWarrantyLiabilityTable_c715881a-ecd2-4903-9726-f4dff315931c" xlink:to="loc_srt_RangeAxis_7a11c91d-b241-4830-b769-b978e71d9044" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_7a11c91d-b241-4830-b769-b978e71d9044_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_7a11c91d-b241-4830-b769-b978e71d9044" xlink:to="loc_srt_RangeMember_7a11c91d-b241-4830-b769-b978e71d9044_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_87e24a97-b682-447d-9aaa-db23458595d3" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_7a11c91d-b241-4830-b769-b978e71d9044" xlink:to="loc_srt_RangeMember_87e24a97-b682-447d-9aaa-db23458595d3" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_4628911c-b9c3-4f40-be84-fd38da277da4" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_87e24a97-b682-447d-9aaa-db23458595d3" xlink:to="loc_srt_MinimumMember_4628911c-b9c3-4f40-be84-fd38da277da4" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_2dfc01a3-628c-444c-9ed8-1719a56a1fee" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_87e24a97-b682-447d-9aaa-db23458595d3" xlink:to="loc_srt_MaximumMember_2dfc01a3-628c-444c-9ed8-1719a56a1fee" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_469f4422-763b-450f-b4e7-c0045e68653d" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ProductWarrantyLiabilityTable_c715881a-ecd2-4903-9726-f4dff315931c" xlink:to="loc_srt_ProductOrServiceAxis_469f4422-763b-450f-b4e7-c0045e68653d" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_469f4422-763b-450f-b4e7-c0045e68653d_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_469f4422-763b-450f-b4e7-c0045e68653d" xlink:to="loc_srt_ProductsAndServicesDomain_469f4422-763b-450f-b4e7-c0045e68653d_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_b8e7ab7d-23e5-40cb-9c6c-3478ed6b59d4" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_469f4422-763b-450f-b4e7-c0045e68653d" xlink:to="loc_srt_ProductsAndServicesDomain_b8e7ab7d-23e5-40cb-9c6c-3478ed6b59d4" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_CommercialProductsMember_10912b90-8ecc-4fac-87f4-2e4e7d080ce2" xlink:href="efoi-20220630.xsd#efoi_CommercialProductsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_b8e7ab7d-23e5-40cb-9c6c-3478ed6b59d4" xlink:to="loc_efoi_CommercialProductsMember_10912b90-8ecc-4fac-87f4-2e4e7d080ce2" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_MMMLEDProductsMember_f60de373-61ef-468c-969c-5e496d2b3c2e" xlink:href="efoi-20220630.xsd#efoi_MMMLEDProductsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_b8e7ab7d-23e5-40cb-9c6c-3478ed6b59d4" xlink:to="loc_efoi_MMMLEDProductsMember_f60de373-61ef-468c-969c-5e496d2b3c2e" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_UVCDProductsMember_56041952-084c-4028-9ceb-761f3b9b35bf" xlink:href="efoi-20220630.xsd#efoi_UVCDProductsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_b8e7ab7d-23e5-40cb-9c6c-3478ed6b59d4" xlink:to="loc_efoi_UVCDProductsMember_56041952-084c-4028-9ceb-761f3b9b35bf" xlink:type="arc" order="2"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesFinancialInstrumentsDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesFinancialInstrumentsDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesFinancialInstrumentsDetails" xlink:type="extended" id="i6d338b899e47401ab016a3744f3734c7_BasisofPresentationandSummaryofSignificantAccountingPoliciesFinancialInstrumentsDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_c2aad1b6-526f-42f0-a986-46b4809c15c8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_c2aad1b6-526f-42f0-a986-46b4809c15c8" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_33e679b1-de8a-4a9b-9adb-8517dec589e3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockPricePerShare"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_33e679b1-de8a-4a9b-9adb-8517dec589e3" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_de165d18-299d-47cc-9509-044f48a7ed30" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_de165d18-299d-47cc-9509-044f48a7ed30" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_5b972726-9c0d-40e0-ab31-44146198906a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_5b972726-9c0d-40e0-ab31-44146198906a" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PaymentsForPlacementAgentCommissions_fdc52dc4-c6db-4c49-8047-96dc08719051" xlink:href="efoi-20220630.xsd#efoi_PaymentsForPlacementAgentCommissions"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_efoi_PaymentsForPlacementAgentCommissions_fdc52dc4-c6db-4c49-8047-96dc08719051" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PaymentsRelatedToExpensesForRegisteredDirectOfferingAndConcurrentPrivatePlacement_4107d6f4-4087-4a26-ad68-55cec252072f" xlink:href="efoi-20220630.xsd#efoi_PaymentsRelatedToExpensesForRegisteredDirectOfferingAndConcurrentPrivatePlacement"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_efoi_PaymentsRelatedToExpensesForRegisteredDirectOfferingAndConcurrentPrivatePlacement_4107d6f4-4087-4a26-ad68-55cec252072f" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PaymentsForClearingFees_908d3c3d-8077-459b-97f1-ff2b85b65954" xlink:href="efoi-20220630.xsd#efoi_PaymentsForClearingFees"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_efoi_PaymentsForClearingFees_908d3c3d-8077-459b-97f1-ff2b85b65954" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_962a1d8b-853a-4e4b-a656-134d7e3ab6af" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_962a1d8b-853a-4e4b-a656-134d7e3ab6af" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts_7e7657c2-dab3-4203-a8a9-ed029e6a6aaa" xlink:href="efoi-20220630.xsd#efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts_7e7657c2-dab3-4203-a8a9-ed029e6a6aaa" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_EstimatedProceedsFromIssuanceOfWarrants_ba144d1e-3a5a-4985-81b6-bd230291360f" xlink:href="efoi-20220630.xsd#efoi_EstimatedProceedsFromIssuanceOfWarrants"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_efoi_EstimatedProceedsFromIssuanceOfWarrants_ba144d1e-3a5a-4985-81b6-bd230291360f" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ClassOfWarrantOrRightWarrantsIssued_3bd314c6-4b8d-4628-8729-be63cf2d0e41" xlink:href="efoi-20220630.xsd#efoi_ClassOfWarrantOrRightWarrantsIssued"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_efoi_ClassOfWarrantOrRightWarrantsIssued_3bd314c6-4b8d-4628-8729-be63cf2d0e41" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ClassOfWarrantOrRightWarrantsIssuedPricePerShare_4658d1cb-b23a-461f-ad9f-f7275a15bc1b" xlink:href="efoi-20220630.xsd#efoi_ClassOfWarrantOrRightWarrantsIssuedPricePerShare"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_efoi_ClassOfWarrantOrRightWarrantsIssuedPricePerShare_4658d1cb-b23a-461f-ad9f-f7275a15bc1b" xlink:type="arc" order="11"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised_3e3524b2-10ce-40e7-b37d-aceab4b32338" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised_3e3524b2-10ce-40e7-b37d-aceab4b32338" xlink:type="arc" order="12"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromWarrantExercises_f3b967b5-4f2a-472a-9a4d-89999a9dc0d3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromWarrantExercises"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_us-gaap_ProceedsFromWarrantExercises_f3b967b5-4f2a-472a-9a4d-89999a9dc0d3" xlink:type="arc" order="13"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_9a479bd5-d3a1-4aaa-aace-9e2b4f630af0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfStockByClassTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_e37adc2c-8156-4e28-a70e-90234b511690" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_9a479bd5-d3a1-4aaa-aace-9e2b4f630af0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_65dcdf88-1b4b-4895-b5c7-9350acc3fe86" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_9a479bd5-d3a1-4aaa-aace-9e2b4f630af0" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_65dcdf88-1b4b-4895-b5c7-9350acc3fe86" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_65dcdf88-1b4b-4895-b5c7-9350acc3fe86_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_65dcdf88-1b4b-4895-b5c7-9350acc3fe86" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_65dcdf88-1b4b-4895-b5c7-9350acc3fe86_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_a84ff1a7-961a-4273-82f2-a8cd2e7cf430" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_65dcdf88-1b4b-4895-b5c7-9350acc3fe86" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_a84ff1a7-961a-4273-82f2-a8cd2e7cf430" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_June2022PrivatePlacementMember_56c78bee-af61-4f35-97fd-196a889f63b8" xlink:href="efoi-20220630.xsd#efoi_June2022PrivatePlacementMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_a84ff1a7-961a-4273-82f2-a8cd2e7cf430" xlink:to="loc_efoi_June2022PrivatePlacementMember_56c78bee-af61-4f35-97fd-196a889f63b8" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_December2021PrivatePlacementMember_bef3be60-5c6c-46b2-8023-16b4ae358d19" xlink:href="efoi-20220630.xsd#efoi_December2021PrivatePlacementMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_a84ff1a7-961a-4273-82f2-a8cd2e7cf430" xlink:to="loc_efoi_December2021PrivatePlacementMember_bef3be60-5c6c-46b2-8023-16b4ae358d19" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_InstitutionalInvestorMember_1915d094-4729-4947-b916-c711b2939e24" xlink:href="efoi-20220630.xsd#efoi_InstitutionalInvestorMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_a84ff1a7-961a-4273-82f2-a8cd2e7cf430" xlink:to="loc_efoi_InstitutionalInvestorMember_1915d094-4729-4947-b916-c711b2939e24" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_January2020InstitutionalInvestorMember_778edb5a-c1d6-4a48-9eaa-664bf4af6b65" xlink:href="efoi-20220630.xsd#efoi_January2020InstitutionalInvestorMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_a84ff1a7-961a-4273-82f2-a8cd2e7cf430" xlink:to="loc_efoi_January2020InstitutionalInvestorMember_778edb5a-c1d6-4a48-9eaa-664bf4af6b65" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_January2020EquityOfferingPrivatePlacementMember_11370978-73f7-4871-bec8-8c1b8b7324f1" xlink:href="efoi-20220630.xsd#efoi_January2020EquityOfferingPrivatePlacementMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_a84ff1a7-961a-4273-82f2-a8cd2e7cf430" xlink:to="loc_efoi_January2020EquityOfferingPrivatePlacementMember_11370978-73f7-4871-bec8-8c1b8b7324f1" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_January2020EquityOfferingMember_dcb40c4a-3212-4f47-807c-8a908dbb30fa" xlink:href="efoi-20220630.xsd#efoi_January2020EquityOfferingMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_a84ff1a7-961a-4273-82f2-a8cd2e7cf430" xlink:to="loc_efoi_January2020EquityOfferingMember_dcb40c4a-3212-4f47-807c-8a908dbb30fa" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_74f38256-2cc0-44b1-aaae-6b5aff52ce2b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_9a479bd5-d3a1-4aaa-aace-9e2b4f630af0" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_74f38256-2cc0-44b1-aaae-6b5aff52ce2b" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_74f38256-2cc0-44b1-aaae-6b5aff52ce2b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_74f38256-2cc0-44b1-aaae-6b5aff52ce2b" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_74f38256-2cc0-44b1-aaae-6b5aff52ce2b_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_82c2b0d3-68f4-410d-98f1-368880a69221" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_74f38256-2cc0-44b1-aaae-6b5aff52ce2b" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_82c2b0d3-68f4-410d-98f1-368880a69221" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PreFundedWarrantsMember_ace658b8-09a1-46d2-816f-890b8ff8d080" xlink:href="efoi-20220630.xsd#efoi_PreFundedWarrantsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_82c2b0d3-68f4-410d-98f1-368880a69221" xlink:to="loc_efoi_PreFundedWarrantsMember_ace658b8-09a1-46d2-816f-890b8ff8d080" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_1f43f209-66cd-4a7c-bc22-38796c9f738a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WarrantMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_82c2b0d3-68f4-410d-98f1-368880a69221" xlink:to="loc_us-gaap_WarrantMember_1f43f209-66cd-4a7c-bc22-38796c9f738a" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/RestructuringNarrativeDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#RestructuringNarrativeDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/RestructuringNarrativeDetails" xlink:type="extended" id="icd0ee26a71e94ddf9a9561cf7d2147a6_RestructuringNarrativeDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_78577db9-5fd7-404a-8532-494fbb5219e3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCosts_e6353db7-551d-4f5f-8805-d8282868d06d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_78577db9-5fd7-404a-8532-494fbb5219e3" xlink:to="loc_us-gaap_RestructuringCosts_e6353db7-551d-4f5f-8805-d8282868d06d" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts_af96d1c3-ee2b-47cd-badb-c8ef9102c5c4" xlink:href="efoi-20220630.xsd#efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_78577db9-5fd7-404a-8532-494fbb5219e3" xlink:to="loc_efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts_af96d1c3-ee2b-47cd-badb-c8ef9102c5c4" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_ec5ae138-7225-475d-863c-9f37d14b189c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_78577db9-5fd7-404a-8532-494fbb5219e3" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_ec5ae138-7225-475d-863c-9f37d14b189c" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_a567997e-eceb-473f-ab0f-9c90e13df956" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_78577db9-5fd7-404a-8532-494fbb5219e3" xlink:to="loc_us-gaap_StockholdersEquity_a567997e-eceb-473f-ab0f-9c90e13df956" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_AdjustmentsToAdditionalPaidInCapitalWarrantReclassified_748d696a-2e35-4274-af2d-d15f94bd3e54" xlink:href="efoi-20220630.xsd#efoi_AdjustmentsToAdditionalPaidInCapitalWarrantReclassified"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_78577db9-5fd7-404a-8532-494fbb5219e3" xlink:to="loc_efoi_AdjustmentsToAdditionalPaidInCapitalWarrantReclassified_748d696a-2e35-4274-af2d-d15f94bd3e54" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_efe21a2d-3485-4c5a-8737-19145f54efb5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_78577db9-5fd7-404a-8532-494fbb5219e3" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_efe21a2d-3485-4c5a-8737-19145f54efb5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_848e63f4-2ee9-45c5-a774-ce503ae96349" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_efe21a2d-3485-4c5a-8737-19145f54efb5" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_848e63f4-2ee9-45c5-a774-ce503ae96349" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_848e63f4-2ee9-45c5-a774-ce503ae96349_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_848e63f4-2ee9-45c5-a774-ce503ae96349" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_848e63f4-2ee9-45c5-a774-ce503ae96349_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_fb8d3744-c9d8-4909-b2db-be9a32c08a86" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_848e63f4-2ee9-45c5-a774-ce503ae96349" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_fb8d3744-c9d8-4909-b2db-be9a32c08a86" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_December2021PrivatePlacementMember_00d3a9c1-85c5-4cd8-9884-de36719550a8" xlink:href="efoi-20220630.xsd#efoi_December2021PrivatePlacementMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_fb8d3744-c9d8-4909-b2db-be9a32c08a86" xlink:to="loc_efoi_December2021PrivatePlacementMember_00d3a9c1-85c5-4cd8-9884-de36719550a8" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_InstitutionalInvestorMember_a339ff04-c04e-4591-824b-521f46a58f5f" xlink:href="efoi-20220630.xsd#efoi_InstitutionalInvestorMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_fb8d3744-c9d8-4909-b2db-be9a32c08a86" xlink:to="loc_efoi_InstitutionalInvestorMember_a339ff04-c04e-4591-824b-521f46a58f5f" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/RestructuringReconciliationofRestructuringLiabilityDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#RestructuringReconciliationofRestructuringLiabilityDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/RestructuringReconciliationofRestructuringLiabilityDetails" xlink:type="extended" id="ib96f7c8b79bf48af95151bd93e676e44_RestructuringReconciliationofRestructuringLiabilityDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_3a897352-a1f7-4d94-a818-dd2f88c9c608" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveRollForward_8c6fcd4c-6b68-4d00-bc16-ef435b875299" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringReserveRollForward"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_3a897352-a1f7-4d94-a818-dd2f88c9c608" xlink:to="loc_us-gaap_RestructuringReserveRollForward_8c6fcd4c-6b68-4d00-bc16-ef435b875299" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_c7f2e3e3-3591-4084-a9af-13702b6cf229" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringReserve"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_8c6fcd4c-6b68-4d00-bc16-ef435b875299" xlink:to="loc_us-gaap_RestructuringReserve_c7f2e3e3-3591-4084-a9af-13702b6cf229" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_40068d4f-a4d6-49ea-b140-feadfbb8b8c3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForRestructuring"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_8c6fcd4c-6b68-4d00-bc16-ef435b875299" xlink:to="loc_us-gaap_PaymentsForRestructuring_40068d4f-a4d6-49ea-b140-feadfbb8b8c3" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_14cfbde5-74ba-45de-ab9c-d1a8cd655897" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringReserve"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_63f72254-6e1f-4fe5-9d22-fbe60bb36240" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_3a897352-a1f7-4d94-a818-dd2f88c9c608" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_63f72254-6e1f-4fe5-9d22-fbe60bb36240" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_a1366778-ab2f-40b7-87b7-b618404e6e18" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_63f72254-6e1f-4fe5-9d22-fbe60bb36240" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_a1366778-ab2f-40b7-87b7-b618404e6e18" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_a1366778-ab2f-40b7-87b7-b618404e6e18_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_a1366778-ab2f-40b7-87b7-b618404e6e18" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_a1366778-ab2f-40b7-87b7-b618404e6e18_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_cf64157c-10d8-42e8-a708-2bd2726242b1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_a1366778-ab2f-40b7-87b7-b618404e6e18" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_cf64157c-10d8-42e8-a708-2bd2726242b1" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FacilityClosingMember_9c8a55c5-3c3f-4feb-bf07-71c1cd50d7b0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FacilityClosingMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_cf64157c-10d8-42e8-a708-2bd2726242b1" xlink:to="loc_us-gaap_FacilityClosingMember_9c8a55c5-3c3f-4feb-bf07-71c1cd50d7b0" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/InventoriesNarrativeDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#InventoriesNarrativeDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/InventoriesNarrativeDetails" xlink:type="extended" id="i97db1da9a4994c069a0c6403cef63b11_InventoriesNarrativeDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryLineItems_523cb2d8-1480-4dfb-8f8d-d9d327d41ef9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_DisposalGroupIncludingDiscontinuedOperationReservedExcessAndObsoleteInventoryPercentage_7e2f32e5-5f39-4905-8847-f4db135c3cf2" xlink:href="efoi-20220630.xsd#efoi_DisposalGroupIncludingDiscontinuedOperationReservedExcessAndObsoleteInventoryPercentage"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_523cb2d8-1480-4dfb-8f8d-d9d327d41ef9" xlink:to="loc_efoi_DisposalGroupIncludingDiscontinuedOperationReservedExcessAndObsoleteInventoryPercentage_7e2f32e5-5f39-4905-8847-f4db135c3cf2" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationInventory1_83d9a03a-f006-40fe-be68-7e4b83ddc3c0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationInventory1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_523cb2d8-1480-4dfb-8f8d-d9d327d41ef9" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationInventory1_83d9a03a-f006-40fe-be68-7e4b83ddc3c0" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryCurrentTable_fea93032-95a9-4c97-a3f4-6660fbf8bb74" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryCurrentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_InventoryLineItems_523cb2d8-1480-4dfb-8f8d-d9d327d41ef9" xlink:to="loc_us-gaap_InventoryCurrentTable_fea93032-95a9-4c97-a3f4-6660fbf8bb74" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_d47c2920-8c86-4d0f-9c49-544aac8a6007" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisposalGroupClassificationAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InventoryCurrentTable_fea93032-95a9-4c97-a3f4-6660fbf8bb74" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_d47c2920-8c86-4d0f-9c49-544aac8a6007" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_d47c2920-8c86-4d0f-9c49-544aac8a6007_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisposalGroupClassificationDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_d47c2920-8c86-4d0f-9c49-544aac8a6007" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_d47c2920-8c86-4d0f-9c49-544aac8a6007_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_a11a41b0-c069-4937-8f2f-f573dbbc0e60" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisposalGroupClassificationDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_d47c2920-8c86-4d0f-9c49-544aac8a6007" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_a11a41b0-c069-4937-8f2f-f573dbbc0e60" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupDisposedOfByMeansOtherThanSaleNotDiscontinuedOperationsSpinoffMember_4b30ac63-b635-4820-8adc-39fbbc1314ef" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisposalGroupDisposedOfByMeansOtherThanSaleNotDiscontinuedOperationsSpinoffMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_a11a41b0-c069-4937-8f2f-f573dbbc0e60" xlink:to="loc_us-gaap_DisposalGroupDisposedOfByMeansOtherThanSaleNotDiscontinuedOperationsSpinoffMember_4b30ac63-b635-4820-8adc-39fbbc1314ef" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/PropertyandEquipmentScheduleofPropertyandEquipmentDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#PropertyandEquipmentScheduleofPropertyandEquipmentDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/PropertyandEquipmentScheduleofPropertyandEquipmentDetails" xlink:type="extended" id="i20c6a18ae80c48239e6e785376c09cca_PropertyandEquipmentScheduleofPropertyandEquipmentDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c8bca3ea-9de7-49ae-8572-5037dc554543" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_2bc13a60-66ef-46cc-a8fa-bd04c45e8ff4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c8bca3ea-9de7-49ae-8572-5037dc554543" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_2bc13a60-66ef-46cc-a8fa-bd04c45e8ff4" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization_36b97f51-9407-4b4f-97ae-d89357a78c11" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c8bca3ea-9de7-49ae-8572-5037dc554543" xlink:to="loc_us-gaap_FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization_36b97f51-9407-4b4f-97ae-d89357a78c11" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization_3d336bb8-05d4-4f8f-afb5-c6c015c785db" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c8bca3ea-9de7-49ae-8572-5037dc554543" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization_3d336bb8-05d4-4f8f-afb5-c6c015c785db" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_32b131d4-445a-4d6a-980b-f855a33c62cd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c8bca3ea-9de7-49ae-8572-5037dc554543" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_32b131d4-445a-4d6a-980b-f855a33c62cd" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_df1f0add-6604-425f-a423-430175c0c553" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c8bca3ea-9de7-49ae-8572-5037dc554543" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_df1f0add-6604-425f-a423-430175c0c553" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_0e4d992a-192c-4254-a607-403955f2503a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c8bca3ea-9de7-49ae-8572-5037dc554543" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_0e4d992a-192c-4254-a607-403955f2503a" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_b62c6071-4fbf-4da1-83ca-8d51168f7528" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Depreciation"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c8bca3ea-9de7-49ae-8572-5037dc554543" xlink:to="loc_us-gaap_Depreciation_b62c6071-4fbf-4da1-83ca-8d51168f7528" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_333f03f2-0f49-4c51-9a66-c92ff888cc62" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c8bca3ea-9de7-49ae-8572-5037dc554543" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_333f03f2-0f49-4c51-9a66-c92ff888cc62" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_42e0a5b0-8924-4101-b7a0-b73b3e77854b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_333f03f2-0f49-4c51-9a66-c92ff888cc62" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_42e0a5b0-8924-4101-b7a0-b73b3e77854b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_42e0a5b0-8924-4101-b7a0-b73b3e77854b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_42e0a5b0-8924-4101-b7a0-b73b3e77854b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_42e0a5b0-8924-4101-b7a0-b73b3e77854b_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1d602db0-6b32-4972-8a39-e4ecfa936689" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_42e0a5b0-8924-4101-b7a0-b73b3e77854b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1d602db0-6b32-4972-8a39-e4ecfa936689" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquipmentMember_b508c5d8-48dc-4d34-b649-80f5bd1a916c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquipmentMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1d602db0-6b32-4972-8a39-e4ecfa936689" xlink:to="loc_us-gaap_EquipmentMember_b508c5d8-48dc-4d34-b649-80f5bd1a916c" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ToolingMember_57179430-c4d3-4de1-b109-8bc05e544644" xlink:href="efoi-20220630.xsd#efoi_ToolingMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1d602db0-6b32-4972-8a39-e4ecfa936689" xlink:to="loc_efoi_ToolingMember_57179430-c4d3-4de1-b109-8bc05e544644" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_VehiclesMember_88ce6727-715c-415e-8c6d-60739bad231d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VehiclesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1d602db0-6b32-4972-8a39-e4ecfa936689" xlink:to="loc_us-gaap_VehiclesMember_88ce6727-715c-415e-8c6d-60739bad231d" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_a01a3479-08a1-46d6-b324-dbb20a37873d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FurnitureAndFixturesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1d602db0-6b32-4972-8a39-e4ecfa936689" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_a01a3479-08a1-46d6-b324-dbb20a37873d" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_ef9be9d8-eaf9-484b-a3bd-e2d0829434ae" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1d602db0-6b32-4972-8a39-e4ecfa936689" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_ef9be9d8-eaf9-484b-a3bd-e2d0829434ae" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_432b4e78-4fd3-4d12-b981-cf17152c8302" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseholdImprovementsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1d602db0-6b32-4972-8a39-e4ecfa936689" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_432b4e78-4fd3-4d12-b981-cf17152c8302" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_RobotsMember_27ee2fa5-aeaf-4494-8670-70a2198c69e3" xlink:href="efoi-20220630.xsd#efoi_RobotsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1d602db0-6b32-4972-8a39-e4ecfa936689" xlink:to="loc_efoi_RobotsMember_27ee2fa5-aeaf-4494-8670-70a2198c69e3" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_8362e157-d57f-4869-9e4d-143c60a0440e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConstructionInProgressMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1d602db0-6b32-4972-8a39-e4ecfa936689" xlink:to="loc_us-gaap_ConstructionInProgressMember_8362e157-d57f-4869-9e4d-143c60a0440e" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_dc433b5e-3bae-4262-a47c-187536a7f1a0" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_333f03f2-0f49-4c51-9a66-c92ff888cc62" xlink:to="loc_srt_RangeAxis_dc433b5e-3bae-4262-a47c-187536a7f1a0" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_dc433b5e-3bae-4262-a47c-187536a7f1a0_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_dc433b5e-3bae-4262-a47c-187536a7f1a0" xlink:to="loc_srt_RangeMember_dc433b5e-3bae-4262-a47c-187536a7f1a0_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_12ab5a8e-8486-415e-b9ef-6a14c700ea82" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_dc433b5e-3bae-4262-a47c-187536a7f1a0" xlink:to="loc_srt_RangeMember_12ab5a8e-8486-415e-b9ef-6a14c700ea82" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_55e3db28-3c69-4b95-bf59-4db938c1ecc0" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_12ab5a8e-8486-415e-b9ef-6a14c700ea82" xlink:to="loc_srt_MinimumMember_55e3db28-3c69-4b95-bf59-4db938c1ecc0" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_6f58a445-34d2-4a75-9da0-783ba2fda1e5" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_12ab5a8e-8486-415e-b9ef-6a14c700ea82" xlink:to="loc_srt_MaximumMember_6f58a445-34d2-4a75-9da0-783ba2fda1e5" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/LeasesNarrativeDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#LeasesNarrativeDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/LeasesNarrativeDetails" xlink:type="extended" id="ic6896ea0994940959170305091db03c5_LeasesNarrativeDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeasedAssetsLineItems_b0e76deb-a243-402c-bc9b-5768f11283b1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeasedAssetsLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_LesseeOperatingLeaseInterestRateEffectiveRate_7781d61d-0955-4ff0-8751-d3bc01e0f1bf" xlink:href="efoi-20220630.xsd#efoi_LesseeOperatingLeaseInterestRateEffectiveRate"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_b0e76deb-a243-402c-bc9b-5768f11283b1" xlink:to="loc_efoi_LesseeOperatingLeaseInterestRateEffectiveRate_7781d61d-0955-4ff0-8751-d3bc01e0f1bf" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseDiscountRate_8802722a-500f-4a6c-8539-5294cad057f0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseDiscountRate"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_b0e76deb-a243-402c-bc9b-5768f11283b1" xlink:to="loc_us-gaap_LesseeOperatingLeaseDiscountRate_8802722a-500f-4a6c-8539-5294cad057f0" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_9dbce219-abc3-4559-98c9-6577118b66cb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_b0e76deb-a243-402c-bc9b-5768f11283b1" xlink:to="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_9dbce219-abc3-4559-98c9-6577118b66cb" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_385d5532-7a39-46bb-b607-af5ab1b695a0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfOperatingLeasedAssetsTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_b0e76deb-a243-402c-bc9b-5768f11283b1" xlink:to="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_385d5532-7a39-46bb-b607-af5ab1b695a0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b9afae12-1c8b-4c1d-aeee-a77672131b25" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_385d5532-7a39-46bb-b607-af5ab1b695a0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b9afae12-1c8b-4c1d-aeee-a77672131b25" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_b9afae12-1c8b-4c1d-aeee-a77672131b25_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b9afae12-1c8b-4c1d-aeee-a77672131b25" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_b9afae12-1c8b-4c1d-aeee-a77672131b25_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_4e07527e-52d8-4ae6-842b-a999f0e2ea86" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b9afae12-1c8b-4c1d-aeee-a77672131b25" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_4e07527e-52d8-4ae6-842b-a999f0e2ea86" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquipmentMember_27c53bf0-3a9c-4463-a44d-a007e2caa6e0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquipmentMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_4e07527e-52d8-4ae6-842b-a999f0e2ea86" xlink:to="loc_us-gaap_EquipmentMember_27c53bf0-3a9c-4463-a44d-a007e2caa6e0" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateMember_2ed169a9-27e8-4e19-bd06-5bed422ed070" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RealEstateMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_4e07527e-52d8-4ae6-842b-a999f0e2ea86" xlink:to="loc_us-gaap_RealEstateMember_2ed169a9-27e8-4e19-bd06-5bed422ed070" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/DebtCreditFacilitiesDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#DebtCreditFacilitiesDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/DebtCreditFacilitiesDetails" xlink:type="extended" id="if4607047d57e48dda0946272c895be3f_DebtCreditFacilitiesDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_e97cf27c-245b-43c1-afab-f45272b77d08" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_DebtInstrumentNumberOfCreditFacilities_d2fd4419-d3f7-4ecd-9142-f1b24bf7888c" xlink:href="efoi-20220630.xsd#efoi_DebtInstrumentNumberOfCreditFacilities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_e97cf27c-245b-43c1-afab-f45272b77d08" xlink:to="loc_efoi_DebtInstrumentNumberOfCreditFacilities_d2fd4419-d3f7-4ecd-9142-f1b24bf7888c" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_27283f5a-e442-4052-948c-59c4088e9335" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_e97cf27c-245b-43c1-afab-f45272b77d08" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_27283f5a-e442-4052-948c-59c4088e9335" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_LineOfCreditFacilityBorrowingCapacityInventoryCostsPercent_cfecaa68-3b4d-4335-9100-bb2eaeb5af39" xlink:href="efoi-20220630.xsd#efoi_LineOfCreditFacilityBorrowingCapacityInventoryCostsPercent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_e97cf27c-245b-43c1-afab-f45272b77d08" xlink:to="loc_efoi_LineOfCreditFacilityBorrowingCapacityInventoryCostsPercent_cfecaa68-3b4d-4335-9100-bb2eaeb5af39" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_LineOfCreditFacilityBorrowingCapacityInventoryValuePercent_c3971f9b-d0a7-4395-a206-397c75dd9511" xlink:href="efoi-20220630.xsd#efoi_LineOfCreditFacilityBorrowingCapacityInventoryValuePercent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_e97cf27c-245b-43c1-afab-f45272b77d08" xlink:to="loc_efoi_LineOfCreditFacilityBorrowingCapacityInventoryValuePercent_c3971f9b-d0a7-4395-a206-397c75dd9511" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_26474dd8-28fb-4f94-9884-ca4468ea6314" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_e97cf27c-245b-43c1-afab-f45272b77d08" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_26474dd8-28fb-4f94-9884-ca4468ea6314" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_DebtInstrumentBaseRateVariable_a8d4645b-fa9d-4499-bfa6-605c3aa075cb" xlink:href="efoi-20220630.xsd#efoi_DebtInstrumentBaseRateVariable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_e97cf27c-245b-43c1-afab-f45272b77d08" xlink:to="loc_efoi_DebtInstrumentBaseRateVariable_a8d4645b-fa9d-4499-bfa6-605c3aa075cb" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_LineOfCreditFacilityMonthlyFacilityFeePercent_ff328c91-8162-4760-957e-e9f9ce837f89" xlink:href="efoi-20220630.xsd#efoi_LineOfCreditFacilityMonthlyFacilityFeePercent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_e97cf27c-245b-43c1-afab-f45272b77d08" xlink:to="loc_efoi_LineOfCreditFacilityMonthlyFacilityFeePercent_ff328c91-8162-4760-957e-e9f9ce837f89" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_LineOfCreditFacilityMonthlyFacilityFee_a0a72367-1c7d-4a05-b4fd-2e82e1807104" xlink:href="efoi-20220630.xsd#efoi_LineOfCreditFacilityMonthlyFacilityFee"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_e97cf27c-245b-43c1-afab-f45272b77d08" xlink:to="loc_efoi_LineOfCreditFacilityMonthlyFacilityFee_a0a72367-1c7d-4a05-b4fd-2e82e1807104" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_LineOfCreditFacilityBorrowingCapacityValueOfAccountsReceivablePercent_d508a24c-1e48-41ac-af30-fa0f19d56049" xlink:href="efoi-20220630.xsd#efoi_LineOfCreditFacilityBorrowingCapacityValueOfAccountsReceivablePercent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_e97cf27c-245b-43c1-afab-f45272b77d08" xlink:to="loc_efoi_LineOfCreditFacilityBorrowingCapacityValueOfAccountsReceivablePercent_d508a24c-1e48-41ac-af30-fa0f19d56049" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_DebtInstrumentInterestRateStatedPercentageCollateralManagementFee_f49339aa-7c83-4627-94bf-abb56241c52a" xlink:href="efoi-20220630.xsd#efoi_DebtInstrumentInterestRateStatedPercentageCollateralManagementFee"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_e97cf27c-245b-43c1-afab-f45272b77d08" xlink:to="loc_efoi_DebtInstrumentInterestRateStatedPercentageCollateralManagementFee_f49339aa-7c83-4627-94bf-abb56241c52a" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LinesOfCreditCurrent_0bd76c28-3c05-4d16-b7b4-93ac1773fb2a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LinesOfCreditCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_e97cf27c-245b-43c1-afab-f45272b77d08" xlink:to="loc_us-gaap_LinesOfCreditCurrent_0bd76c28-3c05-4d16-b7b4-93ac1773fb2a" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnamortizedDebtIssuanceExpense_a37707da-fb57-481e-ad05-52019c8a2db0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UnamortizedDebtIssuanceExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_e97cf27c-245b-43c1-afab-f45272b77d08" xlink:to="loc_us-gaap_UnamortizedDebtIssuanceExpense_a37707da-fb57-481e-ad05-52019c8a2db0" xlink:type="arc" order="11"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_ce997580-09a3-46c0-9d7d-7bda8d8ea685" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_e97cf27c-245b-43c1-afab-f45272b77d08" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_ce997580-09a3-46c0-9d7d-7bda8d8ea685" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_10d67d4d-c3b1-48f3-a7ff-c4e8901e404c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_ce997580-09a3-46c0-9d7d-7bda8d8ea685" xlink:to="loc_us-gaap_CreditFacilityAxis_10d67d4d-c3b1-48f3-a7ff-c4e8901e404c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_10d67d4d-c3b1-48f3-a7ff-c4e8901e404c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_10d67d4d-c3b1-48f3-a7ff-c4e8901e404c" xlink:to="loc_us-gaap_CreditFacilityDomain_10d67d4d-c3b1-48f3-a7ff-c4e8901e404c_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_4a40d4db-3ea5-498b-9485-1cfb8f72bf02" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_10d67d4d-c3b1-48f3-a7ff-c4e8901e404c" xlink:to="loc_us-gaap_CreditFacilityDomain_4a40d4db-3ea5-498b-9485-1cfb8f72bf02" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_e01cb993-c3b5-445a-91a4-7664d5828228" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevolvingCreditFacilityMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_4a40d4db-3ea5-498b-9485-1cfb8f72bf02" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_e01cb993-c3b5-445a-91a4-7664d5828228" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_98595936-67b3-4ee2-89f1-2d43959b4265" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_ce997580-09a3-46c0-9d7d-7bda8d8ea685" xlink:to="loc_us-gaap_DebtInstrumentAxis_98595936-67b3-4ee2-89f1-2d43959b4265" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_98595936-67b3-4ee2-89f1-2d43959b4265_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_98595936-67b3-4ee2-89f1-2d43959b4265" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_98595936-67b3-4ee2-89f1-2d43959b4265_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_c4835c83-a057-45b7-b384-fc6ba75a1ea4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_98595936-67b3-4ee2-89f1-2d43959b4265" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_c4835c83-a057-45b7-b384-fc6ba75a1ea4" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_InventoryFacilityMember_5ded067b-0914-4deb-a509-e45443829473" xlink:href="efoi-20220630.xsd#efoi_InventoryFacilityMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c4835c83-a057-45b7-b384-fc6ba75a1ea4" xlink:to="loc_efoi_InventoryFacilityMember_5ded067b-0914-4deb-a509-e45443829473" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ReceivablesFacilityMember_00246897-e418-4d96-b560-223167844f0f" xlink:href="efoi-20220630.xsd#efoi_ReceivablesFacilityMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c4835c83-a057-45b7-b384-fc6ba75a1ea4" xlink:to="loc_efoi_ReceivablesFacilityMember_00246897-e418-4d96-b560-223167844f0f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_47358b9f-fd00-43c1-8918-9cec85c662b0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_ce997580-09a3-46c0-9d7d-7bda8d8ea685" xlink:to="loc_us-gaap_VariableRateAxis_47358b9f-fd00-43c1-8918-9cec85c662b0" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_47358b9f-fd00-43c1-8918-9cec85c662b0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_47358b9f-fd00-43c1-8918-9cec85c662b0" xlink:to="loc_us-gaap_VariableRateDomain_47358b9f-fd00-43c1-8918-9cec85c662b0_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_eae659f3-3073-44ca-80ca-42dc57f87655" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_47358b9f-fd00-43c1-8918-9cec85c662b0" xlink:to="loc_us-gaap_VariableRateDomain_eae659f3-3073-44ca-80ca-42dc57f87655" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_73b357fe-6463-4452-9d49-093d1625f2c9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_eae659f3-3073-44ca-80ca-42dc57f87655" xlink:to="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_73b357fe-6463-4452-9d49-093d1625f2c9" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_WallStreetJournalHighestPrimeRateMember_6ab6ce65-54b9-447f-a96a-992d078404f7" xlink:href="efoi-20220630.xsd#efoi_WallStreetJournalHighestPrimeRateMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_eae659f3-3073-44ca-80ca-42dc57f87655" xlink:to="loc_efoi_WallStreetJournalHighestPrimeRateMember_6ab6ce65-54b9-447f-a96a-992d078404f7" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/DebtStreetervilleNotesDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#DebtStreetervilleNotesDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/DebtStreetervilleNotesDetails" xlink:type="extended" id="i313083a9b0544a92983a483946b8a59a_DebtStreetervilleNotesDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_95c0af21-25c7-492d-84f3-096c068c5dc5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFaceAmount"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_95c0af21-25c7-492d-84f3-096c068c5dc5" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_ddce11f9-d201-4f44-827f-74dc958e8584" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentUnamortizedDiscount"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_ddce11f9-d201-4f44-827f-74dc958e8584" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_b84048c9-b9fe-449b-a7af-b22751b69db8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_b84048c9-b9fe-449b-a7af-b22751b69db8" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsGross_4e31c39f-6f33-4601-b774-5d2c4edf2147" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredFinanceCostsGross"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:to="loc_us-gaap_DeferredFinanceCostsGross_4e31c39f-6f33-4601-b774-5d2c4edf2147" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_ba7e5594-5cd6-44fe-a225-d86aaa4e2817" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_ba7e5594-5cd6-44fe-a225-d86aaa4e2817" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_DebtInstrumentPrepaymentPremiumPercent_18bf5416-c4fa-4d7b-b6e8-c13dae4e5e30" xlink:href="efoi-20220630.xsd#efoi_DebtInstrumentPrepaymentPremiumPercent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:to="loc_efoi_DebtInstrumentPrepaymentPremiumPercent_18bf5416-c4fa-4d7b-b6e8-c13dae4e5e30" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_DebtPrepaymentMaximumPercentage_41f93789-3da9-4159-92bf-e6e85bf4e420" xlink:href="efoi-20220630.xsd#efoi_DebtPrepaymentMaximumPercentage"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:to="loc_efoi_DebtPrepaymentMaximumPercentage_41f93789-3da9-4159-92bf-e6e85bf4e420" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_DebtInstrumentSubjectToMandatoryRedemptionMaximumAmount_0ae45a3a-9a3c-4f26-b843-ce1501cffdf3" xlink:href="efoi-20220630.xsd#efoi_DebtInstrumentSubjectToMandatoryRedemptionMaximumAmount"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:to="loc_efoi_DebtInstrumentSubjectToMandatoryRedemptionMaximumAmount_0ae45a3a-9a3c-4f26-b843-ce1501cffdf3" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_DebtInstrumentRightToDeferMandatoryRedemptionNumberOfDeferrals_9f15421d-6bba-4ab0-86bc-dbbf838919e7" xlink:href="efoi-20220630.xsd#efoi_DebtInstrumentRightToDeferMandatoryRedemptionNumberOfDeferrals"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:to="loc_efoi_DebtInstrumentRightToDeferMandatoryRedemptionNumberOfDeferrals_9f15421d-6bba-4ab0-86bc-dbbf838919e7" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_NotePayablePercentageIncreaseDueToDeferralOfRedemptionOption_3f6ca2f2-e120-4fad-b6c2-6a2e7f911b86" xlink:href="efoi-20220630.xsd#efoi_NotePayablePercentageIncreaseDueToDeferralOfRedemptionOption"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:to="loc_efoi_NotePayablePercentageIncreaseDueToDeferralOfRedemptionOption_3f6ca2f2-e120-4fad-b6c2-6a2e7f911b86" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_4b27a11b-bb10-4233-aa4d-2d0c92ead485" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_4b27a11b-bb10-4233-aa4d-2d0c92ead485" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_32040897-3148-4760-8606-cf6c69909741" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_32040897-3148-4760-8606-cf6c69909741" xlink:type="arc" order="11"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_DebtInstrumentPercentageIncreaseIfDelistedFromSecurityExchange_59d54b82-cf82-416b-8d68-57bf02018394" xlink:href="efoi-20220630.xsd#efoi_DebtInstrumentPercentageIncreaseIfDelistedFromSecurityExchange"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:to="loc_efoi_DebtInstrumentPercentageIncreaseIfDelistedFromSecurityExchange_59d54b82-cf82-416b-8d68-57bf02018394" xlink:type="arc" order="12"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_bbe0adc1-a025-4532-8f3c-95f876f7d52c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7176b1c5-4a11-4768-8dc1-f6da7c56de83" xlink:to="loc_us-gaap_DebtInstrumentTable_bbe0adc1-a025-4532-8f3c-95f876f7d52c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_c29fed99-ac40-4518-b30f-fe1e6d695b62" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_bbe0adc1-a025-4532-8f3c-95f876f7d52c" xlink:to="loc_us-gaap_DebtInstrumentAxis_c29fed99-ac40-4518-b30f-fe1e6d695b62" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_c29fed99-ac40-4518-b30f-fe1e6d695b62_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_c29fed99-ac40-4518-b30f-fe1e6d695b62" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_c29fed99-ac40-4518-b30f-fe1e6d695b62_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_c35f5f60-6939-419f-9b0d-20368eae304a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_c29fed99-ac40-4518-b30f-fe1e6d695b62" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_c35f5f60-6939-419f-9b0d-20368eae304a" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_A2022StreetervilleNoteMember_bd239ef2-c7a4-47d8-86c4-669e8e8a2c67" xlink:href="efoi-20220630.xsd#efoi_A2022StreetervilleNoteMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c35f5f60-6939-419f-9b0d-20368eae304a" xlink:to="loc_efoi_A2022StreetervilleNoteMember_bd239ef2-c7a4-47d8-86c4-669e8e8a2c67" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_A2021StreetervilleNoteMember_4085adbe-8301-487b-9984-16308222c497" xlink:href="efoi-20220630.xsd#efoi_A2021StreetervilleNoteMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c35f5f60-6939-419f-9b0d-20368eae304a" xlink:to="loc_efoi_A2021StreetervilleNoteMember_4085adbe-8301-487b-9984-16308222c497" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_c0c496ed-eeba-498c-a357-3ccf079b89db" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentRedemptionPeriodAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_bbe0adc1-a025-4532-8f3c-95f876f7d52c" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_c0c496ed-eeba-498c-a357-3ccf079b89db" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_c0c496ed-eeba-498c-a357-3ccf079b89db_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_c0c496ed-eeba-498c-a357-3ccf079b89db" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_c0c496ed-eeba-498c-a357-3ccf079b89db_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_180c2df9-7a28-46fb-91ff-1fe325846daa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_c0c496ed-eeba-498c-a357-3ccf079b89db" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_180c2df9-7a28-46fb-91ff-1fe325846daa" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_61d94acb-1453-4b24-a62b-f2b89e92471d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentRedemptionPeriodOneMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_180c2df9-7a28-46fb-91ff-1fe325846daa" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_61d94acb-1453-4b24-a62b-f2b89e92471d" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_d27ab19d-5aa1-4f6f-b6b2-3ae11d4687f6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentRedemptionPeriodTwoMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_180c2df9-7a28-46fb-91ff-1fe325846daa" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_d27ab19d-5aa1-4f6f-b6b2-3ae11d4687f6" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/DebtPPPLoanDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#DebtPPPLoanDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/DebtPPPLoanDetails" xlink:type="extended" id="i12685b95f9204595abc34d27453e5cf8_DebtPPPLoanDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_3ee07db4-4d2e-4313-bbce-f466fabede24" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLoanOriginations1_9e96d415-cb89-4edb-b1ae-1dc4b351ea09" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromLoanOriginations1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_3ee07db4-4d2e-4313-bbce-f466fabede24" xlink:to="loc_us-gaap_ProceedsFromLoanOriginations1_9e96d415-cb89-4edb-b1ae-1dc4b351ea09" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_a180df0c-5fb2-4891-8b2c-8fe82c561f46" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_3ee07db4-4d2e-4313-bbce-f466fabede24" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_a180df0c-5fb2-4891-8b2c-8fe82c561f46" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_GainLossOnForgivenessOfDebt_7a38ff86-0903-496e-9e06-c1dfa3b81ada" xlink:href="efoi-20220630.xsd#efoi_GainLossOnForgivenessOfDebt"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_3ee07db4-4d2e-4313-bbce-f466fabede24" xlink:to="loc_efoi_GainLossOnForgivenessOfDebt_7a38ff86-0903-496e-9e06-c1dfa3b81ada" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_58eeb925-d384-4622-996b-a7edf6ece02d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_3ee07db4-4d2e-4313-bbce-f466fabede24" xlink:to="loc_us-gaap_DebtInstrumentTable_58eeb925-d384-4622-996b-a7edf6ece02d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_b6dd8c72-749d-48bc-8ace-4b9155dfc699" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_58eeb925-d384-4622-996b-a7edf6ece02d" xlink:to="loc_us-gaap_DebtInstrumentAxis_b6dd8c72-749d-48bc-8ace-4b9155dfc699" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_b6dd8c72-749d-48bc-8ace-4b9155dfc699_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_b6dd8c72-749d-48bc-8ace-4b9155dfc699" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_b6dd8c72-749d-48bc-8ace-4b9155dfc699_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_29dac96f-5795-423d-bcee-5b27e85b39fe" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_b6dd8c72-749d-48bc-8ace-4b9155dfc699" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_29dac96f-5795-423d-bcee-5b27e85b39fe" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PaycheckProtectionProgramCARESActMember_7643f100-d161-4d7c-a826-7eefda71a37f" xlink:href="efoi-20220630.xsd#efoi_PaycheckProtectionProgramCARESActMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_29dac96f-5795-423d-bcee-5b27e85b39fe" xlink:to="loc_efoi_PaycheckProtectionProgramCARESActMember_7643f100-d161-4d7c-a826-7eefda71a37f" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/IncomeTaxesNarrativeDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#IncomeTaxesNarrativeDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended" id="ibafda7a7afd0433fac9680d8f1959177_IncomeTaxesNarrativeDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsLineItems_ef83fea1-34bf-4c8d-bf6e-9e08fe98e3ba" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLossCarryforwardsLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_cab193eb-913f-4906-acac-ce7584c56d20" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwards"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_ef83fea1-34bf-4c8d-bf6e-9e08fe98e3ba" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_cab193eb-913f-4906-acac-ce7584c56d20" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_DeferredTaxAssetsOperatingLossCarryforwardsPortionAvailableAfterApplicationOfIRCSection382Limitations_3a4fbfa8-abd7-4fcf-8275-51eda90660d3" xlink:href="efoi-20220630.xsd#efoi_DeferredTaxAssetsOperatingLossCarryforwardsPortionAvailableAfterApplicationOfIRCSection382Limitations"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_ef83fea1-34bf-4c8d-bf6e-9e08fe98e3ba" xlink:to="loc_efoi_DeferredTaxAssetsOperatingLossCarryforwardsPortionAvailableAfterApplicationOfIRCSection382Limitations_3a4fbfa8-abd7-4fcf-8275-51eda90660d3" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwards_0ec0fb4e-0114-4f24-97be-7ea7f5ba1655" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLossCarryforwards"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_ef83fea1-34bf-4c8d-bf6e-9e08fe98e3ba" xlink:to="loc_us-gaap_OperatingLossCarryforwards_0ec0fb4e-0114-4f24-97be-7ea7f5ba1655" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration_ec71988c-9ba1-4150-a501-cea99bd9405f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_ef83fea1-34bf-4c8d-bf6e-9e08fe98e3ba" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration_ec71988c-9ba1-4150-a501-cea99bd9405f" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsTable_0dab7c0b-01e7-4bf0-a449-5bff9fcfe730" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLossCarryforwardsTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_ef83fea1-34bf-4c8d-bf6e-9e08fe98e3ba" xlink:to="loc_us-gaap_OperatingLossCarryforwardsTable_0dab7c0b-01e7-4bf0-a449-5bff9fcfe730" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_ffb1bb78-6f91-4874-bb15-12c59c1bef21" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OperatingLossCarryforwardsTable_0dab7c0b-01e7-4bf0-a449-5bff9fcfe730" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_ffb1bb78-6f91-4874-bb15-12c59c1bef21" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_ffb1bb78-6f91-4874-bb15-12c59c1bef21_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_ffb1bb78-6f91-4874-bb15-12c59c1bef21" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_ffb1bb78-6f91-4874-bb15-12c59c1bef21_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_c186c742-7ff8-4e6b-86e4-9bea91842c3c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_ffb1bb78-6f91-4874-bb15-12c59c1bef21" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_c186c742-7ff8-4e6b-86e4-9bea91842c3c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_8a1f9a14-0d9c-4832-b6df-2f2b77d52192" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DomesticCountryMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_c186c742-7ff8-4e6b-86e4-9bea91842c3c" xlink:to="loc_us-gaap_DomesticCountryMember_8a1f9a14-0d9c-4832-b6df-2f2b77d52192" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_26031d83-d825-4fcc-baa0-db0da4b100f9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_c186c742-7ff8-4e6b-86e4-9bea91842c3c" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_26031d83-d825-4fcc-baa0-db0da4b100f9" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/StockholdersEquityJune2022andDecember2021PrivatePlacementDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#StockholdersEquityJune2022andDecember2021PrivatePlacementDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/StockholdersEquityJune2022andDecember2021PrivatePlacementDetails" xlink:type="extended" id="iafb56c553293409488e317d997764b56_StockholdersEquityJune2022andDecember2021PrivatePlacementDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f1fcdea3-3f58-45d6-9393-21a1533752c6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_c1ddece3-5199-4324-8c41-1689d5d29f48" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f1fcdea3-3f58-45d6-9393-21a1533752c6" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_c1ddece3-5199-4324-8c41-1689d5d29f48" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_557de3b8-0dfe-45fb-89c3-171f5eb557c6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockPricePerShare"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f1fcdea3-3f58-45d6-9393-21a1533752c6" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_557de3b8-0dfe-45fb-89c3-171f5eb557c6" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_631b576b-a76a-4467-a34f-08499df1b30d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f1fcdea3-3f58-45d6-9393-21a1533752c6" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_631b576b-a76a-4467-a34f-08499df1b30d" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_e8922b8e-2488-477c-87f8-284d4d6e98bb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f1fcdea3-3f58-45d6-9393-21a1533752c6" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_e8922b8e-2488-477c-87f8-284d4d6e98bb" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_EstimatedProceedsFromIssuanceOfWarrants_e219eb63-0925-414a-b2b6-1e24b63d4ced" xlink:href="efoi-20220630.xsd#efoi_EstimatedProceedsFromIssuanceOfWarrants"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f1fcdea3-3f58-45d6-9393-21a1533752c6" xlink:to="loc_efoi_EstimatedProceedsFromIssuanceOfWarrants_e219eb63-0925-414a-b2b6-1e24b63d4ced" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PaymentsForPlacementAgentCommissions_ea35522c-eb12-478a-a9d9-f8298c17e068" xlink:href="efoi-20220630.xsd#efoi_PaymentsForPlacementAgentCommissions"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f1fcdea3-3f58-45d6-9393-21a1533752c6" xlink:to="loc_efoi_PaymentsForPlacementAgentCommissions_ea35522c-eb12-478a-a9d9-f8298c17e068" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PaymentsRelatedToExpensesForRegisteredDirectOfferingAndConcurrentPrivatePlacement_23a2a173-4de3-490d-a2d5-047c9818aaf1" xlink:href="efoi-20220630.xsd#efoi_PaymentsRelatedToExpensesForRegisteredDirectOfferingAndConcurrentPrivatePlacement"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f1fcdea3-3f58-45d6-9393-21a1533752c6" xlink:to="loc_efoi_PaymentsRelatedToExpensesForRegisteredDirectOfferingAndConcurrentPrivatePlacement_23a2a173-4de3-490d-a2d5-047c9818aaf1" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PaymentsForClearingFees_940205ed-fc45-4b55-92c3-31ae856af337" xlink:href="efoi-20220630.xsd#efoi_PaymentsForClearingFees"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f1fcdea3-3f58-45d6-9393-21a1533752c6" xlink:to="loc_efoi_PaymentsForClearingFees_940205ed-fc45-4b55-92c3-31ae856af337" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_b0249b2f-1f98-42b5-a978-905c97aaa135" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f1fcdea3-3f58-45d6-9393-21a1533752c6" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_b0249b2f-1f98-42b5-a978-905c97aaa135" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts_7f36bccd-9be3-4e52-b7de-ab5e15693084" xlink:href="efoi-20220630.xsd#efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f1fcdea3-3f58-45d6-9393-21a1533752c6" xlink:to="loc_efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts_7f36bccd-9be3-4e52-b7de-ab5e15693084" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ClassOfWarrantOrRightWarrantsIssued_9d5a895b-dee0-4c15-b508-71388941e7bd" xlink:href="efoi-20220630.xsd#efoi_ClassOfWarrantOrRightWarrantsIssued"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f1fcdea3-3f58-45d6-9393-21a1533752c6" xlink:to="loc_efoi_ClassOfWarrantOrRightWarrantsIssued_9d5a895b-dee0-4c15-b508-71388941e7bd" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_374e2bab-7041-4609-bb78-93094ddf1138" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f1fcdea3-3f58-45d6-9393-21a1533752c6" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_374e2bab-7041-4609-bb78-93094ddf1138" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_3fb57de2-fa0d-4f9e-9754-2d74c70aa05c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_374e2bab-7041-4609-bb78-93094ddf1138" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_3fb57de2-fa0d-4f9e-9754-2d74c70aa05c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_3fb57de2-fa0d-4f9e-9754-2d74c70aa05c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_3fb57de2-fa0d-4f9e-9754-2d74c70aa05c" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_3fb57de2-fa0d-4f9e-9754-2d74c70aa05c_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_78a5976c-bc50-48c4-9a4f-aeeb186fdfc0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_3fb57de2-fa0d-4f9e-9754-2d74c70aa05c" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_78a5976c-bc50-48c4-9a4f-aeeb186fdfc0" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_December2021PrivatePlacementMember_826b4d98-fb77-467c-8ab0-a024e59eb8db" xlink:href="efoi-20220630.xsd#efoi_December2021PrivatePlacementMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_78a5976c-bc50-48c4-9a4f-aeeb186fdfc0" xlink:to="loc_efoi_December2021PrivatePlacementMember_826b4d98-fb77-467c-8ab0-a024e59eb8db" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_June2022PrivatePlacementMember_4a9381ae-da83-448b-ad0e-ffe5901dcf90" xlink:href="efoi-20220630.xsd#efoi_June2022PrivatePlacementMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_78a5976c-bc50-48c4-9a4f-aeeb186fdfc0" xlink:to="loc_efoi_June2022PrivatePlacementMember_4a9381ae-da83-448b-ad0e-ffe5901dcf90" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_14b23c0e-a7ee-49f7-a936-52c37f2845d3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_374e2bab-7041-4609-bb78-93094ddf1138" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_14b23c0e-a7ee-49f7-a936-52c37f2845d3" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_14b23c0e-a7ee-49f7-a936-52c37f2845d3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_14b23c0e-a7ee-49f7-a936-52c37f2845d3" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_14b23c0e-a7ee-49f7-a936-52c37f2845d3_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_7ee97256-e2f4-4cde-824b-51621cf88944" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_14b23c0e-a7ee-49f7-a936-52c37f2845d3" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_7ee97256-e2f4-4cde-824b-51621cf88944" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PreFundedWarrantsMember_3246b23c-114b-45d2-ad75-19c6b5f0d96b" xlink:href="efoi-20220630.xsd#efoi_PreFundedWarrantsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_7ee97256-e2f4-4cde-824b-51621cf88944" xlink:to="loc_efoi_PreFundedWarrantsMember_3246b23c-114b-45d2-ad75-19c6b5f0d96b" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_dff5de0b-5511-4dae-8b3a-c50e85611498" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WarrantMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_7ee97256-e2f4-4cde-824b-51621cf88944" xlink:to="loc_us-gaap_WarrantMember_dff5de0b-5511-4dae-8b3a-c50e85611498" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/StockholdersEquityJune2021EquityOfferingDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#StockholdersEquityJune2021EquityOfferingDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/StockholdersEquityJune2021EquityOfferingDetails" xlink:type="extended" id="i0038609a081141278bf3e40c9f8450c6_StockholdersEquityJune2021EquityOfferingDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_841e0915-a63e-4d12-af57-dfe1cdc2c671" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_0182faaa-6bf7-45ef-b888-524e67212ddd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_841e0915-a63e-4d12-af57-dfe1cdc2c671" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_0182faaa-6bf7-45ef-b888-524e67212ddd" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_01dec49c-5055-4836-9a33-09a18b747981" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockPricePerShare"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_841e0915-a63e-4d12-af57-dfe1cdc2c671" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_01dec49c-5055-4836-9a33-09a18b747981" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PaymentsForPlacementAgentCommissions_fda488cb-39e2-4fdf-80f2-084eb5f5af4e" xlink:href="efoi-20220630.xsd#efoi_PaymentsForPlacementAgentCommissions"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_841e0915-a63e-4d12-af57-dfe1cdc2c671" xlink:to="loc_efoi_PaymentsForPlacementAgentCommissions_fda488cb-39e2-4fdf-80f2-084eb5f5af4e" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PaymentsRelatedToExpensesForRegisteredDirectOfferingAndConcurrentPrivatePlacement_18a06d3e-5325-4644-9ebc-8a6a58a81fef" xlink:href="efoi-20220630.xsd#efoi_PaymentsRelatedToExpensesForRegisteredDirectOfferingAndConcurrentPrivatePlacement"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_841e0915-a63e-4d12-af57-dfe1cdc2c671" xlink:to="loc_efoi_PaymentsRelatedToExpensesForRegisteredDirectOfferingAndConcurrentPrivatePlacement_18a06d3e-5325-4644-9ebc-8a6a58a81fef" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PaymentsForClearingFees_95477f95-978a-480b-a9b4-bd25e0500d5a" xlink:href="efoi-20220630.xsd#efoi_PaymentsForClearingFees"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_841e0915-a63e-4d12-af57-dfe1cdc2c671" xlink:to="loc_efoi_PaymentsForClearingFees_95477f95-978a-480b-a9b4-bd25e0500d5a" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_887674aa-9bdf-4c0d-9590-fac09d7d17e3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_841e0915-a63e-4d12-af57-dfe1cdc2c671" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_887674aa-9bdf-4c0d-9590-fac09d7d17e3" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts_6097594a-714f-4e47-8941-3008d7cc216c" xlink:href="efoi-20220630.xsd#efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_841e0915-a63e-4d12-af57-dfe1cdc2c671" xlink:to="loc_efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts_6097594a-714f-4e47-8941-3008d7cc216c" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_5dc9a0ff-b1b2-46c1-9b02-b74d36ca6435" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_841e0915-a63e-4d12-af57-dfe1cdc2c671" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_5dc9a0ff-b1b2-46c1-9b02-b74d36ca6435" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_885ce7eb-40f8-4310-9c1c-ea7172083827" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_5dc9a0ff-b1b2-46c1-9b02-b74d36ca6435" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_885ce7eb-40f8-4310-9c1c-ea7172083827" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_885ce7eb-40f8-4310-9c1c-ea7172083827_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_885ce7eb-40f8-4310-9c1c-ea7172083827" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_885ce7eb-40f8-4310-9c1c-ea7172083827_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_06ee08be-cb4b-48f3-9f31-4621d89d0d83" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_885ce7eb-40f8-4310-9c1c-ea7172083827" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_06ee08be-cb4b-48f3-9f31-4621d89d0d83" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_InstitutionalInvestorMember_e4c4939b-fd2a-4f2e-aed5-49018e26a1e4" xlink:href="efoi-20220630.xsd#efoi_InstitutionalInvestorMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_06ee08be-cb4b-48f3-9f31-4621d89d0d83" xlink:to="loc_efoi_InstitutionalInvestorMember_e4c4939b-fd2a-4f2e-aed5-49018e26a1e4" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/StockholdersEquityPreferredStockDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#StockholdersEquityPreferredStockDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/StockholdersEquityPreferredStockDetails" xlink:type="extended" id="i349d2df5a8f04083970f301d75f7bebe_StockholdersEquityPreferredStockDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1167fb78-0c8a-456b-96fb-01ac8ffcfbb1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_NetProceedsFromTheConversionOfConvertibleDebtToPreferredStock_bc78aaff-4590-4b4a-b0e0-b2481d244eb2" xlink:href="efoi-20220630.xsd#efoi_NetProceedsFromTheConversionOfConvertibleDebtToPreferredStock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1167fb78-0c8a-456b-96fb-01ac8ffcfbb1" xlink:to="loc_efoi_NetProceedsFromTheConversionOfConvertibleDebtToPreferredStock_bc78aaff-4590-4b4a-b0e0-b2481d244eb2" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_8247176c-87d3-4e1c-9571-aea97fcd3d57" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1167fb78-0c8a-456b-96fb-01ac8ffcfbb1" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_8247176c-87d3-4e1c-9571-aea97fcd3d57" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_484f86a6-f0a0-4e90-95d3-0c843e5d8f30" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1167fb78-0c8a-456b-96fb-01ac8ffcfbb1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_484f86a6-f0a0-4e90-95d3-0c843e5d8f30" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_139edacc-cffd-455f-be56-4f05055965b1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1167fb78-0c8a-456b-96fb-01ac8ffcfbb1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_139edacc-cffd-455f-be56-4f05055965b1" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_f754af5f-0b85-4a8c-b469-d812d7a4f369" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1167fb78-0c8a-456b-96fb-01ac8ffcfbb1" xlink:to="loc_us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_f754af5f-0b85-4a8c-b469-d812d7a4f369" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_a077364e-bec9-4700-864f-4712c4e67def" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesAuthorized"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1167fb78-0c8a-456b-96fb-01ac8ffcfbb1" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_a077364e-bec9-4700-864f-4712c4e67def" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_fc714613-0536-4c9a-b1c7-c20fd6a526b6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1167fb78-0c8a-456b-96fb-01ac8ffcfbb1" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_fc714613-0536-4c9a-b1c7-c20fd6a526b6" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PercentageOfSeriesAPreferredStockEligibleToVote_e2200ef9-5f8c-4f12-8d44-5960bdc7bf98" xlink:href="efoi-20220630.xsd#efoi_PercentageOfSeriesAPreferredStockEligibleToVote"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1167fb78-0c8a-456b-96fb-01ac8ffcfbb1" xlink:to="loc_efoi_PercentageOfSeriesAPreferredStockEligibleToVote_e2200ef9-5f8c-4f12-8d44-5960bdc7bf98" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_75f0090a-20fe-4ee6-930a-8b8721fd5e05" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1167fb78-0c8a-456b-96fb-01ac8ffcfbb1" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_75f0090a-20fe-4ee6-930a-8b8721fd5e05" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_b84aea90-c6a0-41d6-8543-61f7fdb2df10" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_75f0090a-20fe-4ee6-930a-8b8721fd5e05" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_b84aea90-c6a0-41d6-8543-61f7fdb2df10" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_b84aea90-c6a0-41d6-8543-61f7fdb2df10_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_b84aea90-c6a0-41d6-8543-61f7fdb2df10" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_b84aea90-c6a0-41d6-8543-61f7fdb2df10_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_790d3ba2-423c-4c61-b17f-34631b00ce23" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_b84aea90-c6a0-41d6-8543-61f7fdb2df10" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_790d3ba2-423c-4c61-b17f-34631b00ce23" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_4b9705d3-7bc8-418b-80ea-79748ce92900" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConvertibleDebtMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_790d3ba2-423c-4c61-b17f-34631b00ce23" xlink:to="loc_us-gaap_ConvertibleDebtMember_4b9705d3-7bc8-418b-80ea-79748ce92900" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_54aac1ab-80db-4352-98d8-2434b1d9c2ee" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_75f0090a-20fe-4ee6-930a-8b8721fd5e05" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_54aac1ab-80db-4352-98d8-2434b1d9c2ee" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_54aac1ab-80db-4352-98d8-2434b1d9c2ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_54aac1ab-80db-4352-98d8-2434b1d9c2ee" xlink:to="loc_us-gaap_EquityComponentDomain_54aac1ab-80db-4352-98d8-2434b1d9c2ee_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_98e8fb4d-f8ae-447f-af03-af5c08efa793" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_54aac1ab-80db-4352-98d8-2434b1d9c2ee" xlink:to="loc_us-gaap_EquityComponentDomain_98e8fb4d-f8ae-447f-af03-af5c08efa793" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_21d670eb-bc57-4598-b90b-1b0624dfe2fd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_98e8fb4d-f8ae-447f-af03-af5c08efa793" xlink:to="loc_us-gaap_PreferredStockMember_21d670eb-bc57-4598-b90b-1b0624dfe2fd" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_55faf8cd-f0f6-4f82-8eef-eb1169f0cf25" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_98e8fb4d-f8ae-447f-af03-af5c08efa793" xlink:to="loc_us-gaap_CommonStockMember_55faf8cd-f0f6-4f82-8eef-eb1169f0cf25" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_5c316498-9fa8-4253-9373-53560e3b816b" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_75f0090a-20fe-4ee6-930a-8b8721fd5e05" xlink:to="loc_srt_CounterpartyNameAxis_5c316498-9fa8-4253-9373-53560e3b816b" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_5c316498-9fa8-4253-9373-53560e3b816b_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_5c316498-9fa8-4253-9373-53560e3b816b" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_5c316498-9fa8-4253-9373-53560e3b816b_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_8ec97805-14bf-4594-b11e-561a78e4f71c" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_5c316498-9fa8-4253-9373-53560e3b816b" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_8ec97805-14bf-4594-b11e-561a78e4f71c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_FusionParkLLCMember_01bf9712-b5bc-4582-be14-1a351d086840" xlink:href="efoi-20220630.xsd#efoi_FusionParkLLCMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_8ec97805-14bf-4594-b11e-561a78e4f71c" xlink:to="loc_efoi_FusionParkLLCMember_01bf9712-b5bc-4582-be14-1a351d086840" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_BrilliantStartEnterpriseIncMember_b6278a22-4e0e-4e89-888b-fc02b3a33e7b" xlink:href="efoi-20220630.xsd#efoi_BrilliantStartEnterpriseIncMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_8ec97805-14bf-4594-b11e-561a78e4f71c" xlink:to="loc_efoi_BrilliantStartEnterpriseIncMember_b6278a22-4e0e-4e89-888b-fc02b3a33e7b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_5ad97bca-1c1e-46a5-8ccd-691cbf2bd086" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_75f0090a-20fe-4ee6-930a-8b8721fd5e05" xlink:to="loc_us-gaap_StatementClassOfStockAxis_5ad97bca-1c1e-46a5-8ccd-691cbf2bd086" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_5ad97bca-1c1e-46a5-8ccd-691cbf2bd086_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_5ad97bca-1c1e-46a5-8ccd-691cbf2bd086" xlink:to="loc_us-gaap_ClassOfStockDomain_5ad97bca-1c1e-46a5-8ccd-691cbf2bd086_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_0be798bc-8ca2-4182-aa14-64307597ac10" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_5ad97bca-1c1e-46a5-8ccd-691cbf2bd086" xlink:to="loc_us-gaap_ClassOfStockDomain_0be798bc-8ca2-4182-aa14-64307597ac10" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_280d954a-e514-4874-8414-50f5fcbb6b02" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConvertiblePreferredStockMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_0be798bc-8ca2-4182-aa14-64307597ac10" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_280d954a-e514-4874-8414-50f5fcbb6b02" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/StockholdersEquityJune2020EquityOfferingDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#StockholdersEquityJune2020EquityOfferingDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/StockholdersEquityJune2020EquityOfferingDetails" xlink:type="extended" id="ibc9d2bd741864e0384932fa98cba8fd8_StockholdersEquityJune2020EquityOfferingDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_a702d49b-818b-4761-8835-892b71d8c98d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_a702d49b-818b-4761-8835-892b71d8c98d" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_9f0a82c1-d7b4-4123-b304-195eb4f43e7d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockPricePerShare"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_9f0a82c1-d7b4-4123-b304-195eb4f43e7d" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_e9f44819-9563-4b58-940a-2a28e216095c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_e9f44819-9563-4b58-940a-2a28e216095c" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_d05980e3-33d8-4b98-affd-391448d90b36" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_d05980e3-33d8-4b98-affd-391448d90b36" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ClassOfWarrantOrRightWarrantsIssuedPricePerShare_8b62b9d2-4fb5-4546-b0f0-eff1465d1706" xlink:href="efoi-20220630.xsd#efoi_ClassOfWarrantOrRightWarrantsIssuedPricePerShare"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_efoi_ClassOfWarrantOrRightWarrantsIssuedPricePerShare_8b62b9d2-4fb5-4546-b0f0-eff1465d1706" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PaymentsForPlacementAgentCommissions_772d31ac-b40f-4de9-9e65-f7e7757b1e9c" xlink:href="efoi-20220630.xsd#efoi_PaymentsForPlacementAgentCommissions"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_efoi_PaymentsForPlacementAgentCommissions_772d31ac-b40f-4de9-9e65-f7e7757b1e9c" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PaymentsRelatedToExpensesForRegisteredDirectOfferingAndConcurrentPrivatePlacement_b0789b38-77ca-423f-aa47-7ccfa4567c02" xlink:href="efoi-20220630.xsd#efoi_PaymentsRelatedToExpensesForRegisteredDirectOfferingAndConcurrentPrivatePlacement"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_efoi_PaymentsRelatedToExpensesForRegisteredDirectOfferingAndConcurrentPrivatePlacement_b0789b38-77ca-423f-aa47-7ccfa4567c02" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PaymentsForClearingFees_29ad8e79-164d-4b6d-a649-f5798f57ea4d" xlink:href="efoi-20220630.xsd#efoi_PaymentsForClearingFees"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_efoi_PaymentsForClearingFees_29ad8e79-164d-4b6d-a649-f5798f57ea4d" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_9662a986-fee8-4967-950e-c05527ccd819" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_9662a986-fee8-4967-950e-c05527ccd819" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts_dcaad231-fdf3-4a54-8fdc-62823f4291d7" xlink:href="efoi-20220630.xsd#efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_efoi_ProceedsFromTheIssuanceOfCommonStockAndWarrantsNetOfIssuanceCosts_dcaad231-fdf3-4a54-8fdc-62823f4291d7" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ClassOfWarrantOrRightWarrantsIssued_3754d325-3ed8-4c09-b1b4-083fe92ee5d8" xlink:href="efoi-20220630.xsd#efoi_ClassOfWarrantOrRightWarrantsIssued"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_efoi_ClassOfWarrantOrRightWarrantsIssued_3754d325-3ed8-4c09-b1b4-083fe92ee5d8" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_EstimatedProceedsFromIssuanceOfWarrants_08531e27-9399-4641-95d8-6b02bc5a1150" xlink:href="efoi-20220630.xsd#efoi_EstimatedProceedsFromIssuanceOfWarrants"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_efoi_EstimatedProceedsFromIssuanceOfWarrants_08531e27-9399-4641-95d8-6b02bc5a1150" xlink:type="arc" order="11"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised_beb57792-e5bc-42f1-b527-88e004a8c0f3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised_beb57792-e5bc-42f1-b527-88e004a8c0f3" xlink:type="arc" order="12"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromWarrantExercises_26732d4b-0805-4192-9098-a58158826754" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromWarrantExercises"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_us-gaap_ProceedsFromWarrantExercises_26732d4b-0805-4192-9098-a58158826754" xlink:type="arc" order="13"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_28f2a2c5-bc96-47e3-88fa-e6799af4eb20" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_12bda6b1-4305-45a1-9bd0-7e70812182c7" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_28f2a2c5-bc96-47e3-88fa-e6799af4eb20" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_e5017518-b8a8-47f7-80cc-556e40495b5d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_28f2a2c5-bc96-47e3-88fa-e6799af4eb20" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_e5017518-b8a8-47f7-80cc-556e40495b5d" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_e5017518-b8a8-47f7-80cc-556e40495b5d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_e5017518-b8a8-47f7-80cc-556e40495b5d" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_e5017518-b8a8-47f7-80cc-556e40495b5d_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7c285d3e-9733-4aca-867c-498fe9fe282a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_e5017518-b8a8-47f7-80cc-556e40495b5d" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7c285d3e-9733-4aca-867c-498fe9fe282a" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_January2020InstitutionalInvestorMember_628fd39b-3a56-437e-a79e-ebca873374d9" xlink:href="efoi-20220630.xsd#efoi_January2020InstitutionalInvestorMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7c285d3e-9733-4aca-867c-498fe9fe282a" xlink:to="loc_efoi_January2020InstitutionalInvestorMember_628fd39b-3a56-437e-a79e-ebca873374d9" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_InstitutionalInvestorMember_8db35e26-68f5-4702-b7cf-12b3f0ff5b4a" xlink:href="efoi-20220630.xsd#efoi_InstitutionalInvestorMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7c285d3e-9733-4aca-867c-498fe9fe282a" xlink:to="loc_efoi_InstitutionalInvestorMember_8db35e26-68f5-4702-b7cf-12b3f0ff5b4a" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_January2020EquityOfferingMember_3b320e11-223d-40dd-a5dd-920c6d58dccb" xlink:href="efoi-20220630.xsd#efoi_January2020EquityOfferingMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7c285d3e-9733-4aca-867c-498fe9fe282a" xlink:to="loc_efoi_January2020EquityOfferingMember_3b320e11-223d-40dd-a5dd-920c6d58dccb" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_January2020EquityOfferingPrivatePlacementMember_d465906c-9011-4d0a-85eb-53cfba556acb" xlink:href="efoi-20220630.xsd#efoi_January2020EquityOfferingPrivatePlacementMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7c285d3e-9733-4aca-867c-498fe9fe282a" xlink:to="loc_efoi_January2020EquityOfferingPrivatePlacementMember_d465906c-9011-4d0a-85eb-53cfba556acb" xlink:type="arc" order="3"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/StockholdersEquityOutstandingWarrantsfromtheJanuary2020EquityOfferingDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#StockholdersEquityOutstandingWarrantsfromtheJanuary2020EquityOfferingDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/StockholdersEquityOutstandingWarrantsfromtheJanuary2020EquityOfferingDetails" xlink:type="extended" id="idbb1263692fe4a67a0a513f15e362246_StockholdersEquityOutstandingWarrantsfromtheJanuary2020EquityOfferingDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ff77f018-2c61-46f5-b17d-bcd628a194eb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_ClassOfWarrantOrRightWarrantsIssued_e6387a84-db03-41c8-b34c-28b331360255" xlink:href="efoi-20220630.xsd#efoi_ClassOfWarrantOrRightWarrantsIssued"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ff77f018-2c61-46f5-b17d-bcd628a194eb" xlink:to="loc_efoi_ClassOfWarrantOrRightWarrantsIssued_e6387a84-db03-41c8-b34c-28b331360255" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_ae53a747-884a-4d39-84d3-c6e722c90269" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockPricePerShare"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ff77f018-2c61-46f5-b17d-bcd628a194eb" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_ae53a747-884a-4d39-84d3-c6e722c90269" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_2db07bb9-aac9-43f4-8eed-cde089ee75d1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ff77f018-2c61-46f5-b17d-bcd628a194eb" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_2db07bb9-aac9-43f4-8eed-cde089ee75d1" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_dc657baa-acf9-42b6-babf-7726bc8cb8fc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ff77f018-2c61-46f5-b17d-bcd628a194eb" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_dc657baa-acf9-42b6-babf-7726bc8cb8fc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_f916f841-cff2-42a6-b311-377da15269b1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_dc657baa-acf9-42b6-babf-7726bc8cb8fc" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_f916f841-cff2-42a6-b311-377da15269b1" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_f916f841-cff2-42a6-b311-377da15269b1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_f916f841-cff2-42a6-b311-377da15269b1" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_f916f841-cff2-42a6-b311-377da15269b1_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_24fd08c6-a514-4e00-9706-512ef0e05627" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_f916f841-cff2-42a6-b311-377da15269b1" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_24fd08c6-a514-4e00-9706-512ef0e05627" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_January2020EquityOfferingMember_3a86c023-d0a3-4533-95f7-e61944c9f709" xlink:href="efoi-20220630.xsd#efoi_January2020EquityOfferingMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_24fd08c6-a514-4e00-9706-512ef0e05627" xlink:to="loc_efoi_January2020EquityOfferingMember_3a86c023-d0a3-4533-95f7-e61944c9f709" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_InstitutionalInvestorMember_9563cd28-01de-434d-b74b-fb29167da4ec" xlink:href="efoi-20220630.xsd#efoi_InstitutionalInvestorMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_efoi_January2020EquityOfferingMember_3a86c023-d0a3-4533-95f7-e61944c9f709" xlink:to="loc_efoi_InstitutionalInvestorMember_9563cd28-01de-434d-b74b-fb29167da4ec" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_January2020InstitutionalInvestorMember_e8caaf70-2563-4dae-9645-cd767908993f" xlink:href="efoi-20220630.xsd#efoi_January2020InstitutionalInvestorMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_efoi_January2020EquityOfferingMember_3a86c023-d0a3-4533-95f7-e61944c9f709" xlink:to="loc_efoi_January2020InstitutionalInvestorMember_e8caaf70-2563-4dae-9645-cd767908993f" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_January2020EquityOfferingPrivatePlacementMember_0f560c03-f4d7-47fa-9f4e-586e449957ea" xlink:href="efoi-20220630.xsd#efoi_January2020EquityOfferingPrivatePlacementMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_efoi_January2020EquityOfferingMember_3a86c023-d0a3-4533-95f7-e61944c9f709" xlink:to="loc_efoi_January2020EquityOfferingPrivatePlacementMember_0f560c03-f4d7-47fa-9f4e-586e449957ea" xlink:type="arc" order="3"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/StockholdersEquityStockBasedCompensationDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#StockholdersEquityStockBasedCompensationDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/StockholdersEquityStockBasedCompensationDetails" xlink:type="extended" id="iddfa56acf62a43798f7dae8ec6707c35_StockholdersEquityStockBasedCompensationDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_03663a36-d3c1-4476-8b4f-c2321aa89e19" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_536a0c20-931c-4e9a-b2ed-82059608522d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_03663a36-d3c1-4476-8b4f-c2321aa89e19" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_536a0c20-931c-4e9a-b2ed-82059608522d" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_c3a6156e-371b-4339-ad68-c419a21cf49d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_03663a36-d3c1-4476-8b4f-c2321aa89e19" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_c3a6156e-371b-4339-ad68-c419a21cf49d" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_a38dc991-56dd-4e12-b902-8188b35477c0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_03663a36-d3c1-4476-8b4f-c2321aa89e19" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_a38dc991-56dd-4e12-b902-8188b35477c0" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_7c2510be-c124-4ffe-bd6d-ea7f92cb8d02" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_03663a36-d3c1-4476-8b4f-c2321aa89e19" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_7c2510be-c124-4ffe-bd6d-ea7f92cb8d02" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_8eccf81a-9267-4f7c-af9e-292b4c4e5f41" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_7c2510be-c124-4ffe-bd6d-ea7f92cb8d02" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_8eccf81a-9267-4f7c-af9e-292b4c4e5f41" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_8eccf81a-9267-4f7c-af9e-292b4c4e5f41_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_8eccf81a-9267-4f7c-af9e-292b4c4e5f41" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_8eccf81a-9267-4f7c-af9e-292b4c4e5f41_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_6c282be2-2ba5-4d8f-ada6-c198af17a450" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_8eccf81a-9267-4f7c-af9e-292b4c4e5f41" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_6c282be2-2ba5-4d8f-ada6-c198af17a450" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_9f761c0d-47ea-4944-9f33-bf3f8f0673c2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostOfSalesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_6c282be2-2ba5-4d8f-ada6-c198af17a450" xlink:to="loc_us-gaap_CostOfSalesMember_9f761c0d-47ea-4944-9f33-bf3f8f0673c2" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_c99a58d6-960e-4e65-8d01-69dfe44ca31d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_6c282be2-2ba5-4d8f-ada6-c198af17a450" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_c99a58d6-960e-4e65-8d01-69dfe44ca31d" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_66a29d7b-fc4d-4bf2-8182-1b8381aae6ab" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_6c282be2-2ba5-4d8f-ada6-c198af17a450" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_66a29d7b-fc4d-4bf2-8182-1b8381aae6ab" xlink:type="arc" order="2"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/StockholdersEquityEstimatesUtilizedDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#StockholdersEquityEstimatesUtilizedDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/StockholdersEquityEstimatesUtilizedDetails" xlink:type="extended" id="i41ae0a8971e340aa938323e196be95a9_StockholdersEquityEstimatesUtilizedDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f0affbb9-f900-4baa-bb1f-8a4610556899" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_e0fad7a8-a005-4c5a-bfb9-9b64b1f78c61" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f0affbb9-f900-4baa-bb1f-8a4610556899" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_e0fad7a8-a005-4c5a-bfb9-9b64b1f78c61" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice_3369d770-892e-41b5-a2d6-5c29001ed5e4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f0affbb9-f900-4baa-bb1f-8a4610556899" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice_3369d770-892e-41b5-a2d6-5c29001ed5e4" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_802760a6-31a2-4d2d-b370-3c013f7ecc20" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f0affbb9-f900-4baa-bb1f-8a4610556899" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_802760a6-31a2-4d2d-b370-3c013f7ecc20" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_5117898e-d3f1-4e57-8f7a-1f2e7f578a86" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f0affbb9-f900-4baa-bb1f-8a4610556899" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_5117898e-d3f1-4e57-8f7a-1f2e7f578a86" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_7e12a2c1-e01b-4057-9cf2-755f2dcc3cfc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f0affbb9-f900-4baa-bb1f-8a4610556899" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_7e12a2c1-e01b-4057-9cf2-755f2dcc3cfc" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_0b99676d-0ba2-4aea-b875-6a36200061a6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f0affbb9-f900-4baa-bb1f-8a4610556899" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_0b99676d-0ba2-4aea-b875-6a36200061a6" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_0b5c91d8-6735-49dc-81b4-12eb640002ba" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f0affbb9-f900-4baa-bb1f-8a4610556899" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_0b5c91d8-6735-49dc-81b4-12eb640002ba" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_34115a75-4083-415a-b2b9-30ef5a620b66" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_0b5c91d8-6735-49dc-81b4-12eb640002ba" xlink:to="loc_us-gaap_AwardTypeAxis_34115a75-4083-415a-b2b9-30ef5a620b66" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_34115a75-4083-415a-b2b9-30ef5a620b66_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_34115a75-4083-415a-b2b9-30ef5a620b66" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_34115a75-4083-415a-b2b9-30ef5a620b66_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ec0ff9c0-ac8e-4a77-b108-b7b51f35e6dc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_34115a75-4083-415a-b2b9-30ef5a620b66" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ec0ff9c0-ac8e-4a77-b108-b7b51f35e6dc" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_a8414d4d-2fe8-460c-8b49-e6d46865c818" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ec0ff9c0-ac8e-4a77-b108-b7b51f35e6dc" xlink:to="loc_us-gaap_EmployeeStockOptionMember_a8414d4d-2fe8-460c-8b49-e6d46865c818" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/StockholdersEquityRestrictedStockUnitsDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#StockholdersEquityRestrictedStockUnitsDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/StockholdersEquityRestrictedStockUnitsDetails" xlink:type="extended" id="icd67ee69d9a44acfa780b39f3d65bced_StockholdersEquityRestrictedStockUnitsDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4444c57e-618e-44ef-a27b-622e6c760e56" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_109cf2ce-b187-4226-b80e-8eab042dd9a9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4444c57e-618e-44ef-a27b-622e6c760e56" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_109cf2ce-b187-4226-b80e-8eab042dd9a9" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_3eac0018-7bfa-41bf-93b2-cc8d0e5bfc07" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_109cf2ce-b187-4226-b80e-8eab042dd9a9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_3eac0018-7bfa-41bf-93b2-cc8d0e5bfc07" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_68878aac-5d3d-4f45-9372-c3a12a99f2a3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_109cf2ce-b187-4226-b80e-8eab042dd9a9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_68878aac-5d3d-4f45-9372-c3a12a99f2a3" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_4f2a43a5-168e-4499-98ed-875145706d2e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_109cf2ce-b187-4226-b80e-8eab042dd9a9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_4f2a43a5-168e-4499-98ed-875145706d2e" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_915e0bd3-36f1-4fa9-9509-af3d114039f3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cf784b26-8531-4153-bac3-de2a0285dd61" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4444c57e-618e-44ef-a27b-622e6c760e56" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cf784b26-8531-4153-bac3-de2a0285dd61" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_35d954cc-0e29-466e-bf96-e918974435ce" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cf784b26-8531-4153-bac3-de2a0285dd61" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_35d954cc-0e29-466e-bf96-e918974435ce" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_9cc755c7-35e8-4af6-a619-6a072c718e03" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cf784b26-8531-4153-bac3-de2a0285dd61" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_9cc755c7-35e8-4af6-a619-6a072c718e03" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_106f211a-3ad3-4589-adbb-04e8dc214266" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cf784b26-8531-4153-bac3-de2a0285dd61" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_106f211a-3ad3-4589-adbb-04e8dc214266" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_3a506235-fd36-4b32-b2aa-78facf5d9d79" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_3872e4bc-08b4-4aeb-936f-2d434c2eb305" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4444c57e-618e-44ef-a27b-622e6c760e56" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_3872e4bc-08b4-4aeb-936f-2d434c2eb305" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_b180a780-c7b1-412c-828e-fe7dfb5f28f3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_3872e4bc-08b4-4aeb-936f-2d434c2eb305" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_b180a780-c7b1-412c-828e-fe7dfb5f28f3" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_07b87802-9291-46fb-8685-b3c399b0f700" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4444c57e-618e-44ef-a27b-622e6c760e56" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_07b87802-9291-46fb-8685-b3c399b0f700" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_87c16706-4854-4181-a527-ca9cf96d3ef2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_07b87802-9291-46fb-8685-b3c399b0f700" xlink:to="loc_us-gaap_AwardTypeAxis_87c16706-4854-4181-a527-ca9cf96d3ef2" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_87c16706-4854-4181-a527-ca9cf96d3ef2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_87c16706-4854-4181-a527-ca9cf96d3ef2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_87c16706-4854-4181-a527-ca9cf96d3ef2_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0c9153a3-e376-4331-9d9d-21f63c6661d7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_87c16706-4854-4181-a527-ca9cf96d3ef2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0c9153a3-e376-4331-9d9d-21f63c6661d7" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_b56e0281-73bd-4cbc-a174-422a070b5e2d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0c9153a3-e376-4331-9d9d-21f63c6661d7" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_b56e0281-73bd-4cbc-a174-422a070b5e2d" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.energyfocusinc.com/role/OtherIncomeDetails" xlink:type="simple" xlink:href="efoi-20220630.xsd#OtherIncomeDetails"/>
<link:definitionLink xlink:role="http://www.energyfocusinc.com/role/OtherIncomeDetails" xlink:type="extended" id="if1162baac16e4d238237bc6ab860e4d7_OtherIncomeDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_c89b44fb-b4ce-4227-b3dc-fcc22793bfaa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PayrollTaxCreditEmployeeRetentionCreditUnderTheCARESAct_26bd70bc-fe3d-44f8-aa30-b2fcd855d54c" xlink:href="efoi-20220630.xsd#efoi_PayrollTaxCreditEmployeeRetentionCreditUnderTheCARESAct"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c89b44fb-b4ce-4227-b3dc-fcc22793bfaa" xlink:to="loc_efoi_PayrollTaxCreditEmployeeRetentionCreditUnderTheCARESAct_26bd70bc-fe3d-44f8-aa30-b2fcd855d54c" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PayrollTaxCreditEmployeeRetentionCreditUnderTheCARESActCurrent_8ef61ac2-114c-4613-8d30-0b5bc7b57266" xlink:href="efoi-20220630.xsd#efoi_PayrollTaxCreditEmployeeRetentionCreditUnderTheCARESActCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c89b44fb-b4ce-4227-b3dc-fcc22793bfaa" xlink:to="loc_efoi_PayrollTaxCreditEmployeeRetentionCreditUnderTheCARESActCurrent_8ef61ac2-114c-4613-8d30-0b5bc7b57266" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLoanOriginations1_a77d05df-4848-41f0-aa83-9e2a5a65a04f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromLoanOriginations1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c89b44fb-b4ce-4227-b3dc-fcc22793bfaa" xlink:to="loc_us-gaap_ProceedsFromLoanOriginations1_a77d05df-4848-41f0-aa83-9e2a5a65a04f" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_d3ed5a03-3c92-4d6e-841c-be9d477795dc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c89b44fb-b4ce-4227-b3dc-fcc22793bfaa" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_d3ed5a03-3c92-4d6e-841c-be9d477795dc" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_GainLossOnForgivenessOfDebt_10224f65-e4e8-434b-a7b7-b643b3c9a994" xlink:href="efoi-20220630.xsd#efoi_GainLossOnForgivenessOfDebt"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c89b44fb-b4ce-4227-b3dc-fcc22793bfaa" xlink:to="loc_efoi_GainLossOnForgivenessOfDebt_10224f65-e4e8-434b-a7b7-b643b3c9a994" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_2bc8609f-2e07-4b98-a9f3-7e29a692b445" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c89b44fb-b4ce-4227-b3dc-fcc22793bfaa" xlink:to="loc_us-gaap_DebtInstrumentTable_2bc8609f-2e07-4b98-a9f3-7e29a692b445" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_465d08a2-817a-48ac-b22d-de51101c97fa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_2bc8609f-2e07-4b98-a9f3-7e29a692b445" xlink:to="loc_us-gaap_DebtInstrumentAxis_465d08a2-817a-48ac-b22d-de51101c97fa" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_465d08a2-817a-48ac-b22d-de51101c97fa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_465d08a2-817a-48ac-b22d-de51101c97fa" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_465d08a2-817a-48ac-b22d-de51101c97fa_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_4f637c38-dec3-4826-ae98-7b8f0c34c620" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_465d08a2-817a-48ac-b22d-de51101c97fa" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_4f637c38-dec3-4826-ae98-7b8f0c34c620" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_efoi_PaycheckProtectionProgramCARESActMember_3286482c-8951-42e5-b330-63e86c87cc2b" xlink:href="efoi-20220630.xsd#efoi_PaycheckProtectionProgramCARESActMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_4f637c38-dec3-4826-ae98-7b8f0c34c620" xlink:to="loc_efoi_PaycheckProtectionProgramCARESActMember_3286482c-8951-42e5-b330-63e86c87cc2b" xlink:type="arc" order="0"/>
</link:definitionLink>
</link:linkbase>

12 Previous Filings that this Filing References

  As Of               Filer                 Filing    For·On·As Docs:Size             Issuer                      Filing Agent

 6/24/22  Energy Focus, Inc./DE             8-K:5,9     6/22/22   11:382K
 6/06/22  Energy Focus, Inc./DE             8-K:1,3,7,9 6/03/21   14:902K
 4/25/22  Energy Focus, Inc./DE             8-K:1,2,9   4/21/22   12:411K
 6/11/20  Energy Focus, Inc./DE             8-K:3,5,7,9 6/11/20    3:92K
 5/18/20  Energy Focus, Inc./DE             8-K:5,9     5/12/20   13:448K
 3/24/20  Energy Focus, Inc./DE             10-K       12/31/19   92:8.5M
 5/30/19  Energy Focus, Inc./DE             8-K:1,3,4,5 5/21/19    3:116K
 4/01/19  Energy Focus, Inc./DE             8-K:1,2,3,5 3/29/19    8:1M
 7/27/15  Energy Focus, Inc./DE             8-K:5,9     7/22/15    2:320K                                   Workiva Inc Wde… FA01/FA
 7/16/14  Energy Focus, Inc./DE             8-K:5,9     7/15/14    7:594K                                   RDG Filings/FA
11/13/13  Energy Focus, Inc./DE             10-Q        9/30/13   76:7.6M                                   RDG Filings/FA
 5/10/07  Energy Focus, Inc./DE             10-Q        3/31/07    6:427K                                   Toppan Merrill/FA
↑Top
Filing Submission 0000924168-22-000071   –   Alternative Formats (Word / Rich Text, HTML, Plain Text, et al.)
Copyright © 2024 Fran Finnegan & Company LLC – All Rights Reserved.
About — Privacy — Redactions — Help — Thu., May 9, 9:00:33.2am ET