LED外文文献精.docx

1、LED外文文献精LED LUMINAIRE LIFETIME:Recommendations for Testing and Reporting Solid State Lighting Product Quality Initiative FIRST EDITION MAY 2010NextGenerationLightingIndustryAlliancewiththeU.S.DepartmentofEnergyINTRODUCTIONUNDERSTANDINGSSLLUMINAIRELIFETIMESurprisinglytomany,thetruereliabilityandlifet

2、imeoflightemittingdiode(LEDlightingsystemsiscurrentlyunknown.Evenworse,lumenmaintenancevaluesofLEDdevicesarewidelyusedasaproxyforthelifetimeofanLEDlightingsystem,whichismisleadingsincelightdegradationorlumenmaintenanceisbutonecomponentofthereliabilityofaluminaire.Formanymanufacturersthisapproachcann

3、otsimplybeascribedtooverlyambitiousmarketingefforts,butrathertodependenceonanecdotalnumbersintheabsenceofrealdata.Inaddition,wecanimputesimpleignoranceintakingspecificationsatfacevaluewhichmayormaynotliveuptoclaims.ItisntjustabouttheLED.GoodLEDscanbeincorporatedintopoorlyengineeredproductsandturnthe

4、Methuselahoflightingintotheexponentof“livefast,dieyoung.”ThepromiseofLEDlifetimeisoftenpresentedintermsofhoursandyearsbutwithlittlebackgrounddatatosupportanythingbeyondvacuouspromises.Thestatementof100,000hoursofLEDluminairelifetimehasgivenwaytotherealizationthatthereislittleconsistency,verylittlepu

5、blisheddata,andfewhardfactsaroundsocalledluminairelifetimenumbers.ThesituationisbetterattheLEDpackagelevel,wherereputablemanufacturershavethousandsofhoursofdataundervaryingconditions.Butthisisnotenough.Tomanufacturersandspecifiersinthesolidstatelighting(SSLcommunity,thedawningrealizationisthatweneed

6、toworktogethertowardsunderstandingtheissuessurroundingtruelifetimeandreliability.Weneedtobeginbycataloguingsuchfailuresanddevelopinggoodmodelsforunderlyingfailuremechanisms.Thisprocessofunderstandingandexplanationisverycommonintechnologicalprogress.Steamenginesexistedlongbeforedeepunderstandingofthe

7、rmodynamicprocesses.WithLEDs,wehaveasubstantialheadstartontheunderlyingphysicsandmanyyearsofexperienceinbothlightingandsemiconductorsaswellasreliabilityofrelatedproducts.Thereisnoreasonnottobeginthisjourneyandeveryreasontostart.Wewillfigurethisout,findreliabilitymethodsandmetrics,andlearntheunderlyi

8、ngrootcausesoffailure.Butwithoutdata,experimentsandmodels,itisallconjecture.Weneedaprogramtodrivetoreliabilitymetrics.WHATTHISGUIDEISANDISNOTThisguideisasetofrecommendationsforreportinganddemonstratingreliabilityintermsofluminaireproductlifetime.Initially,wesoughttoprovideguidancefortheLightingFacts

9、CM program,whichgivesusers,retailers,andmanufacturersacommonshortformreportingmechanismtoimprovethequalityofsolidstatelightingproductsonthemarket.TheLightingFactslabelprovidesasummaryofkeyperformancecriteriabutdoesnotincludelifetime,forwhichtherehavebeennumerousrequests.Ideally,itwouldbetheadditiono

10、fasinglenumber,e.g.,“eightyears.”ButSSLproductlifetimeneedstobeconsideredacombinationofconventionalfailuremechanismsaswellasagradualdeclineoflightoutputovertime.Describingitisnotsimple;demonstratingitisdifficultandexpensive.So,wehavecometoappreciatetheimportanceofgatheringthefullstrengthoftheSSLcomm

11、unitytoaddressthiscriticalissue.Thisguideispurposefullyentitled“FirstEdition.”Indevelopingtheseinitialguidelines,thecommitteeLED Luminaire Lifetime Recommendations, May 2010Page 2recognizesthatthereremainmanyincompleteareasofknowledge,andweintendtopursueandimprovetheserecommendationsovertime.Thesere

12、commendationshavebeendevelopedbyaworkinggroupundertheU.S.DepartmentofEnergySolidStateLightingprogram.ThisgroupisundertheguidanceoftheSSLQualityAdvocatesoversightcommittee,ajointbodyofDOEandtheNextGenerationLightingIndustryAlliance(NGLIA.ThereliabilityandlifetimeworkinggroupiscomposedofmembersoftheNG

13、LIAaswellasotherexpertsinreliability,lighting,andLEDtechnology.Assuch,thisguideisnotanacceptedinternationalstandard.Rather,itismeanttoprovidestandardsbodieswithrecommendationsfortheirworkinsupportingtheneedsoftheSSLcommunity.Thesestandardsorganizationswillultimatelydeterminethedetailsofthemethodstom

14、easureandreportthereliabilityofSSLluminaireproducts.Thisdocumentcoversonlyluminairelifetimei.e.,changeovertimeinnormaloperationandnotinitialperformancecriteriaorproductconsistency.InitialperformancecriteriaforLEDluminaireshavebeenseparatelydiscussedintheDecember2008publicationReporting LED Luminaire

15、 Product Performance, foundontheDOESSLWebsiteat.TYPESOFFAILURESENCOUNTEREDAnLEDluminaireisinmanywaysmorecomplexthanatraditionallightingfixture.It isanelectromechanicalsystemthatincludes,inadditiontotheessentiallightemittingsource,provisionsforheattransfer,electricalcontrol,opticalconditioning,mechan

16、icalsupport,andprotection,aswellasaestheticdesignelements.BecausetheLEDsthemselvesareexpectedtohavelonglife,alloftheseothercomponents,adhesives,andothermaterialsmustbeequallylonglived,or,totheextenttheyarenot,theywilllimitLED Luminaire Lifetime Recommendations, May 2010Page 3Figure 1:Totalsystemorlu

17、minairereliabilityistheproductofalloftheindividualreliabilityconsiderationsasfollows:R Luminaire =RLEDs *ROptical *RPCB *RFinish *RMechanical *R Thermal RHousing *RGaskets *RSealants *RElectrica l*RDriver *R Manufacturing .SOURCE:PHILIPSHADCOthesystemlifetime.WhileLEDsdonotradiateheat,withcurrentpro

18、ductshalformoreoftheinputenergymaybeconvertedtoheatthatmustbeconductedawayfromthediodes.Thissituationrequiresareliable,heatconductingassembly,beitmechanicaloradhesive,inadditiontoaheatsinkcomponentormeansforfurtherconduction.Forproperoperation,thepowersupplyandelectronicsmustprovideawellcontrolledDC

19、drivecurrentandpossiblyothercontrolfeatures,andmustnotfailforthelifeoftheproduct.Anyopticalcomponentsmustbeabletowithstandyearsofexposuretointenselightandpossiblyheatwithoutyellowing,cracking,orothersignificantdegradation.Reflectingmaterialsneedtostayinplaceandmaintaintheiropticalefficiencies.Evenif

20、thedesignitselfhasaddressedalloftheseissues,questionsofpropermanufacturingremain.Wastheepoxyproperlymixed?Wasanessentialheattransmittingpasteomitted?Werethewirebondsproperlymade?Anyofthefailuremechanismsinherentinelectronicassemblies,andmanyothers,mayapplytoanLEDluminaire.Figure1,above,isanattemptto

21、visualizethislargerscopeofSSLreliability.Forthebestlifetimeinawelldesignedandproperlyassembledluminaire,theprincipalfailuremechanismshouldbelumendepreciationagradualreductionoflightoutputfromthepackagedLEDovertime.Butothermechanismscouldcomeintoplay.OneLEDvendorhasreportedthattheprincipalcausesforcu

22、stomercomplaintsinvolveeithertheuseofchemicalsintheluminairethatareincompatiblewiththeLEDorthedriveroverstressingtheLED.Thesearedesignissues,butequallyimportantareearlyfailuresofothercomponentsorsubsystemsormanufacturingdefects.Theseadditionalfailuremechanismswillalwayspersisttosomedegreeandwillusua

23、llyleadtocatastrophicfailure,buttheymaysometimessimplyacceleratelumendepreciation.Animportantmessageofthisguideisthatthesemechanismsmustbeaccountedforindescribingproductlife.THEROLEOFWARRANTIESGiventheearlystageofLEDlightingtechnology,itisdifficulttoaccuratelypredictproductlifetime.Warrantiesprovide

24、ameansforthepotentialbuyertoreducerisk.Whilethisdocumentprovidessomeguidanceonwhatmightbeincludedinawarranty,itisultimatelythemanufacturersdecisiononhowbesttoprovidethisprotectionandhowmuchrisktotakeindoingso.Thewarrantymaylogicallybeshorterthantheclaimedlifetimeasdefinedbelow.Astherewillbeadistribu

25、tionoftimesoffailuresforanyproduct,thedegreeofriskonthepartofthemanufacturerdependsonthelevelofconfidenceintheprojectedlifetimeandtheamountofvariationinthatdistribution.LUMENLIFETIMERECOMMENDEDDEFINITIONOFLIFETIMEForconventionaltechnologies,the“ratedaveragelamplife”isthepointatwhichhalfthelampscease

26、toemitlight.Allsourcesloselightoutputovertime,butgenerallynotmorethat1520percentovertheratedlamplifeasdefinedbycomplete,lightsoutfailure.AwelldesignedLEDpackage,however,wouldtypicallyhaveaverylongratedlife,asconventionallydefined,but,becauseitissolong,wouldalsohavemorelumendepreciationoverthatlifeth

27、anconventionaltechnologies.Accordingly,weneedanewapproach.Whateverthestatedlifetimeofanylightingproduct,itisastatistical measureoftheperformanceofagivendesign.ForanindividualLEDpackage,lifetimehastypicallybeenconsideredtobethehoursofoperationatwhichthelightoutputhasfallento70percentofitsoriginalvalue(“L 70”.LED Luminaire Lifetime Recommendations, May 2010Page 4Lifetimeistypicallyreportedasthemediantimetofailureofapopulationofdiodesundernormaloperatingconditions,called“B 50. ”Inotherwords,afterthisper