LEDLuminaires

Whitepaper

Evaluatingperformanceof

LEDbased

luminaires

IEC

Specificationsincompliance

Create

awareness

EvaluatingperformanceofLEDbasedluminaires

Avoidcomparingapplesandpears

InrecentyearstherehasbeenasignificantincreaseintheuseofLEDbasedluminaires.Initially,therewerenouniversalstandardsavailabletomeasureorcomparetheperformanceofLEDbasedlightingproducts.Thissituationhasbeencompoundedbynewandunprovenentrantsfloodingintothemarket,somemakingdubiousclaimsabouttheirproducts’performance.ThereisalotofconfusionamongcustomersaboutwhichLEDsystemstochoose.

Inthisregard,themainchallengefortheprofessionalmarketistoimprovethewayusersofLEDbasedluminaires,suchasspecifiers,lightingdesigners,technicalengineersandpolicymakers,evaluatetheperformanceclaimsofdifferentLEDluminairemanufacturerswhenpreparinglightingprojectsortenderspecifications.

Todaytheyoftencompare–unwittingly–appleswithpears.

Thiswhitepaperisintendedtobringclarityandtoenableevaluationofmanufacturers’performanceclaimsbyexplainingthedifferent‘initial’and‘overtime’performancecriteriaforLEDbasedluminaireslaiddowninrecentIECperformancestandards.

PhilipsProfessionalLightingSolutionsbelievesina3-stepapproachtocreatefulltransparencyinthemarket:

1.ProvideproductperformancespecificationsincompliancewithappropriateIECstandards;

2.CreateawarenessamongstusersofLEDbasedluminairesonhowqualitycriteriacanhelptocompareandestablishconfidence;

3.Worktowardsindependentthird-partyperformanceverificationforLEDbasedluminaires.

NOTE:

Guidancetowardslike-for-likecomparisonbasedonIECperformancestandardsisexpectedtobewidelyadoptedinEurope.

Performanceverification

Figure1–3-stepapproach

1.1Standardizedqualitycriteria–bringingordertothe

confusion

Asthingsstandatpresent,evaluatingLEDsystemsiscomplex.Therearetwomainreasonsforthis:

a.Differentmanufacturersusedifferenttechnicaldefinitionstodescribetheperformanceoftheirproducts,thusmakingthemdifficulttocompare.

b.Thetechnicaldesignofaproductcanmakeatremendousdifferenceintermsofperformance.EveniftwoluminairesarebasedonexactlythesameLEDs,theirperformancecanbewildlydifferentbecauseofdesignchoicesmade.

Ifwelook,inthetablebelow,atefficacy(expressedinlumensperwatt)forexample,wecanseethatthedesignoftheproductcanmakealargedifferencetothesystemperformanceoftheluminaire.Theeffectivenessoftheheatmanagement,thedriverandtheopticscanallmakeorbreaktheefficacyofthetotalLEDbasedluminaire.

LED

chip

Thermal

design

Driver

Optics

Maintenance

at5000hrs

Efficiency

after

2years

160lm/W

95%

152lm/W

90%

137lm/W

85%

116lm/W

98%

114lm/W

160lm/W

85%

136lm/W

70%

95lm/W

50%

48lm/W

60%

29lm/W

Figure2–Impactdesignchoicesonperformance

Whenevaluatingperformanceclaimsfromdifferentmanufacturers:

a.Applyastandardizedsetofqualitycriteriaforcomparison;

b.OnlyevaluateproductsthathavebeenmeasuredincompliancewithappropriateIECstandards.

Thiswillallowyoutojudgecomparisonclaimsonanequal,like-for-likebasis–appleswithapples,sotospeak,ratherthanappleswithpears.

2ComparingthelifetimeperformanceofLEDbasedluminaires

abrupt

completefailure

ofLED-based

luminaire

gradual

or

lumendepreciation

ofLED-based

luminaire

LEDbasedluminaires

graduallightoutputdegradation

abruptlightoutputdegradation

named:

TimetoAbruptFailure

(LoCy)

2.IECperformancecriteria

Both‘initial’and‘overtime’performancehavetobeevaluatedinordertohaveconfidencehowLEDbasedluminaireswillperformandhowlongtheywillsustaintheirratedcharacteristicsovertheiryearsofoperation.Atpresent,itcanbedifficulttoknowwhototrustorwhattobelieve.

StandardizationofperformancerequirementsisanimportantfirststeptowardsfulltransparencyregardingtheperformanceofLEDbasedluminairesusedintheprofessionalmarket.Therefore,theIECrecentlydevelopedandpublishedspecificperformancestandardsforLEDbasedluminaires.

Thesestandardsdescribehowtomeasure‘initial’performanceandprovidealifetimemetricfor‘overtime’performance.

Itshouldbenotedthatinitialproductspecificationswilltypicallybemeasured,whereasperformanceovertimewillbecalculatedusingtheIEClifetimemetricforLEDbasedlightingproducts.

Producttype

Safetystandard

Performancestandard

LEDcontrolgear

IEC61347-2-13Ed.2.0

Publication2014

IEC62384Ed.1.1

Publication2011

LEDlamps

IEC62560Ed.1.0

Publication2011

IEC62612Ed.1.0

Publication2013

LEDmodules

IEC62031Ed.1.1

Publication2012

IEC62717Ed.1.0

Publication2014

LEDluminaires

IEC60598-1Ed.8.0

Publication2014

IEC62722-2-1Ed.1.0

Publication2014

Figure3–OverviewIECstandardsLEDbasedproducts

WhatPhilipsLightingpublishes

oninitialperformance

TobenefitfromourstandarddevelopmentworkintheIEC,initialperformancespecificationsforallPhilipsProfessionalLightingSolutionsEuropeLEDbased(general)lightingluminairesaremeasuredincompliancewiththeappropriateIECperformancestandards.

1.Initialratedinputpower(inW)

2.Initialratedluminousflux(inlm)

3.InitialLEDluminaireefficacy(inlm/W)

4.Luminousintensitydistribution

5.InitialCorrelatedColorTemperature(CCT)inK

6.InitialratedColorRenderingIndex(CRI)

7.Initialratedchromaticityco-ordinatevalueandexpectedtolerance(x,y)<xSDCM

InitialspecificationsofallLEDbasedluminairesarespecifiedatanambienttemperatureof25°C.

2.2IEC‘overtime’performancecriteria

Therearetworelevant‘overtime’performancevaluestobeconsideredrelatedtogradualandabruptlightoutputdegradationofaLEDbasedluminaireatratedlife.

new

LEDluminaire

100%

Figure4–Overtimeperformance

Graduallightoutputdegradationrelatestothelumenmaintenanceofaluminaireovertime.Ittellsyouhowmuchoftheinitiallumenoutputoftheluminaireismaintainedafteracertainperiodoftime.Thelumendepreciationcanbeacombinationofdegradationofopticalelementsused,individualLEDsgivinglesslightandindividualLEDsgivingnolightatall.

AbruptlightoutputdegradationdescribesthesituationwheretheLEDbasedluminairenolongergivesanylightatallbecausethesystem,oracriticalcomponenttherein,hasfailed.

TheIEClifetimemetricforLEDbasedluminairesspecifiesUsefulLifeandTimetoAbruptFailure.

named:

UsefulLife

(LxBy)

Figure5–IEClifetimemetric

ComparingthelifetimeperformanceofLEDbasedluminaires3

Relative

LuminousFlux

80

80

80

80

80

80

80

90

90

90

80

70

70

70

75

75

75

95

95

65

65

85

85

85

85

100

60

85

75

75

50%ofthesamplearebelowthetargetvalue

80

85

85

80

80

80

80

80

85

90

90

90

85

85

95

95

60

100

90

75

50%ofthesampleareabovethetargetvalue

Average=80

Lognormal

Curve

2.2.1Graduallightoutputdegradation/UsefulLife

Agradualloweringofthelightoutputandlossofefficiency

ThegraduallightoutputdegradationofapopulationofLEDbasedlightingproductsatacertainpointintimeiscalledUsefulLifeandisgenerallyexpressedasLxBy.UsefulLifedescribesthelumenmaintenanceofaLEDbasedluminaireovertime.

UsefulLifeisexpressedasLxByandmeanslengthoftimeduringwhichy%ofapopulationofoperatingLEDbasedluminairesofthesametypefailtoprovideatleastx%oftheinitialluminousflux.‘Lx’describesthelumenmaintenance:L80meansthattheluminairesofthisspecifictypestillgive80%oftheirinitiallightoutput.

‘By’describesforwhatpercentageofthepopulationthatistrue.TheexampleL80B50reflectstheage(inhours)atwhich50%ofthepopulationhavefailedparametrically.ParametricallyinthiscasemeansaLEDbasedluminaireproducinglesslightthan80%ofitsinitialfluxbutstilloperating.

Ifwetakeacloserlookatatypicalcurveshowinghowlightoutputdecreaseswithtime,wecanreadoffthepointintimewherethelightoutputhasdecreasedtoacertainvalue:

100%

90%

80%

40k50k60k

UsefulLife(hours)

However,tounderstandtheUsefulLifeoftherespectiveLEDbasedluminaires,weneedtoinvestigatewhatisactuallyhappeningatthatpoint.

Whatwedoismeasureawholebatchofproductsandobtainarangeofvalues:

85

75

75

70

75

85

65

80

95

95

80

80

80

60

70

80

60

60

75

80

80

90

85

70

85

85

100

75

75

55

60

65

60

90

%ofinitialflux

Whenweaveragealltheproductswehavemeasuredwecreateapointonourdepreciationcurve.Infact,someoftheproductswillbeabovethataverageandsomebelow.

Theywillnotallbethesamevalue.Solet’srearrangeourdatainamoremeaningfulway:

Median=80

%ofinitialflux

Nowwehavearrangedallourdatasowecanseehowmanyoftheproductsarebelowandhowmanyareabovetheaverage.Itisusefultolookatthemedian,whichisthepointonthegraphwherewehavethesamenumberofpointsabovethemedianasbelowit.

WithLEDsthedistributionislogarithmicforLEDlumendecay.Withsuchadistribution,themedianisclosetotheaverage.ThisissignificantaswewillusetheAverageforourdesigncalculationsandtheMedianforpredictinglifebeyondmeasurements.

Inthisexamplethemedianis80andwehaveasmanypointsabovethemedianasbelowit.Wesaythatthelifeisthetimetowhichtheaverageis80%oftheinitialaveragevalue.

80

75

75

80

70

70

70

75

65

65

75

%ofinitialflux

Lightoutputlowerthanthetargetvalue(inthiscase80)iscalleda‘parametricfailure’becausetheproductproduceslesslightbutstilloperates.

Ifwenowplacethisdatabackonourgraphthenweseethattheaverageisat80%andwehave50%parametricfailuresand50%stilloperatingaboveourratedvalueof80%.

4ComparingthelifetimeperformanceofLEDbasedluminaires

Relative

LuminousFlux

Relative

LuminousFlux

Relative

LuminousFlux

L80

B10

100%90%80%70%

active

&

passive

cooling

system

reliability

optical

materials

.

80

80

UsefulLife(hours)

100%90%80%70%

40k50k60k

B50

L80

IntheIECthisisdefinedastheUsefulLife,andweusetheLxtermtoquantifytheaveragevalueandtheBytotellushowmanyareabovetheaverageandhowmanybelow.InthisexamplewewouldsaythattheUsefulLife(L80B50)=50,000hours.UsefulLifethereforehastocontainboththe

‘L’andthe‘B’component.

Wemaydecidethathaving50%ofoursamplebelowtheaverageistoomuchandwewouldwanttoconsiderasmallerpercentage.Ifwewant,say,10%ofourbatchbelowtheaveragethenthetimetoachievethiswillbeless.

InthisexamplewewouldsaythattheUsefulLife(L80B10)=45,000hours.

100%

90%

80%

70%

UsefulLife(hours)40k45k50k60k

However,forgeneralapplicationswewouldnormallytakeytobe50:

L80

80

B50

40k50k60k

UsefulLife(hours)

2.2.2Abruptlightoutputdegradation/TimetoAbrupt

Failure

Anabruptdeclineinlight

outputduetobreakdown

orfailureoftheproduct

oranyofthecomponents

inthesystem

Besideslumenmaintenance(UsefulLife),thereareotherfactorstoconsiderwhenevaluatingperformanceoverlife.

LEDbasedluminairesandmodulesaresophisticatedproductsconsistingofmanycomponents.Animportantparameterthatshouldbeconsideredwithexpectedlonglifeissystemreliability.ALEDbasedluminairewilllastaslongasthecomponentusedwiththeshortestlife.ThereareseveralcriticalcomponentsofaLEDbasedluminairethatinfluencethesystemreliability

package&

inter-connects

LED

mechanical

connections

gasket

sealings

electronics

Figure5––CriticalcomponentsLEDbasedluminaire

TheIEClifetimemetricthereforealsospecifiesTimetoAbruptFailure,whichtakesintoaccountfailuremodesofcriticalcomponentsintheLEDbasedluminairedesign.

TheabruptlightoutputdegradationofapopulationofLEDbasedlightingproductsatacertainpointintimeiscalledTimetoAbruptFailureandisexpressedasL0Cy.TimetoAbruptFailuredescribesthesituationwheretheLEDbasedluminairenolongergivesanylightatall.

‘Lx’describesthelumenmaintenance:L0meansthattheLEDbasedluminairesofthiscertaintypegive0%oftheirinitiallightoutput.‘Cy’describesforwhatpercentageofthepopulationthatistrue.

TheexampleL0C10reflectstheage(inhours)atwhich10%ofthepopulationhavefailedabruptly.

Inthisspecificcasetheaverageandthemedianvalueswill

bethesame,sowedefinetheRatedMedianUsefulLifeLx.

Inthiscasewedon’tneedtousethe‘B’termaswithmedian

yisalways50.

RatedMedianUsefulLife,orRatedLifetimeinthenew

IECgeneraldefinition,isthevaluemarkedonproduct

datasheets,leafletsorwebsite.

ComparingthelifetimeperformanceofLEDbasedluminaires5

%Survivors

100%

90%

80%

100%

92%

80%

Ifwetakeacloserlookatafailurecurve,wecanseewhatpercentageoffailureswehaveatagiventime:

100%

90%

80%

10k20k30k40k50k60k

TimetoAbruptFailure(hours)

However,tounderstandtheTimetoAbruptFailureoftherespectiveLEDbasedluminaires,weneedtoinvestigatewhatisactuallyhappeningatthatpoint.

Takingacloserlookatourdatawecanseemoredetail:

65

80

85

75

75

70

75

85

0

75

75

55

0

95

95

80

80

80

60

70

80

60

60

90

85

70

85

85

80

80

60

65

0

90

90

%ofinitialflux

WithinoursamplebatchofLEDproductswecanseethatsomehavefailedcompletelyorabruptly.Thismaybeduetoamechanicalfailure,driverfailureoranythingthatwouldcauseabruptfailure.

Ifweorderthisdatainasimilarwayaswedidbeforewecanseethatthefailuresareapercentageofthetotal:

80

80

80

80

80

80

90

90

90

80

70

70

95

95

85

85

85

85

75

75

0

0

100

80

70

85

75

75

75

0

%ofinitialflux

Soatanygivenpointonourfailurecurvewesimplyplotthe

percentageoffailurescomparedwiththeoriginalsample

andnotethetimeatwhichthisoccurs:

%Survivors

80

80

80

10k20k30k40k53k60k

TimetoAbruptFailure(hours)

Notethathereweareonlyconcernedwithabruptfailures

andnotfailureduetolossoflight.

Wecallthisthe‘timetoabruptfailure’orCy.Inthisexample

theTimetoAbruptFailure(C10)=53,000hours.

NowwecanlookataspecificfailurethatoccursattheRatedMedianUsefulLife:

%Survivors

80

10k20k30k40k50k60k

TimetoAbruptFailure(hours)

TheRatedAbruptFailureValue(AFV)isthepercentageof

LEDbasedlightingproductsthatfailtooperateattheRated

MedianUsefulLifeLx.Inthisexample,theRatedMedian

UsefulLifeis50,000hoursandtheRatedAbruptFailure

Valueis8%.

Unfortunately,theindustryhasnotyetreachedconsensusonwhatcriticalcomponentshavetobetakenintoaccountwhencalculatingTimetoAbruptFailure.Therefore,PhilipsLightinghasdecidednottopublishthisvalueaslongasthereisariskofapple-to-pearcomparison.

ComparingthelifetimeperformanceofLEDbasedluminaires6

2.2.3Insummary–performanceovertime

Luminairelifeisalwaysacombinationofgradualandabrupt

lightdegradation.Notethatluminairelifeclaimsmustalways

bespecifiedtogetherwithaspecificambienttemperature,

numberofburninghoursandassociatedswitchingcycles.

Asmentionedabove,thedesignoftheLEDbasedluminaire

canhaveasignificantimpactontheluminaireperformance,

includingitslifetime.

ItisthereforeimportanttorealizethatdataprovidedbyLED

orLEDboardsupplierscannotsimplybetranslatedone-to-

oneasLEDbasedluminaireperformancedata.Therefore,we

needtobewaryofclaimssuchas“theseluminairesusethe

sameLEDssothereforetheir(over-time)performanceisthe

same”.

Itisalsoimportanttorememberthatover-timeperformance

valuesarepredictionsratherthanmeasurements.As

theUsefulLifeandTimetoAbruptFailureofLEDbased

luminairesaresolong,itisnotpossibleformanufacturersto

measurethesebeforelaunchingnewproducts.Instead,they

useshortermeasurementsandextrapolatethosetoarriveat

predictions.

Sincethereisnotyetanystandardinplacethatdescribes

howthesepredictionsorextrapolationsshouldbedone,the

qualityofthesepredictionsvarieswildly.TheIEConlyde-

scribesalifetimemetricforLEDbasedproductsatthispoint:

whichparametersshouldbestatedintermsofUsefulLife

andTimetoAbruptFailure,butnothowtocalculatethese.

Philipshasdevelopedabest-in-classtooltocalculateUseful

LifeandTimetoAbruptFailureforLEDbasedluminaires.

Calculationsarebasedonreal-lifeendurancetestdataof

LEDboar