LED固态照明入门介绍资料_精品文档Word文档格式.doc
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LED固态照明入门介绍资料_精品文档Word文档格式.doc
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Solidstatelighting(SSL)referstosolidstatelightemittingdeviceswhichdonotutilizefilimentsorelectronarcstreamstoproducelight.ThemostreadilyrecognizableSSLproductstodayutilizelight-emittingdiodes(LEDs),whichproducephotons
(light)directlyfromthepassageofelectronsfromonematerialwithintheconductivedevicetoanother.OthersformsofLEDsincludeorganiclight-emittingdiodes(OLEDs)whichuseorganicmaterialsbutareotherwisesimilartoLEDsandpolymerlight-emittingdiodes(PLEDs),whicharemadefromflexiblematerials.OtherformsofSSLproductsincludeCathodluminescence-wherelightisgivenoffbyamaterialbombardedbyelectronsgeneratingheatwhichcausesthematerialtoemitphotons(light),orElectrolumenescencewherevisiblelightisproducedbyasubstanceexposedtoanelectricfieldwithoutanythermalenergygeneration.Theterm"
solidstate"
referstothefactthatlightisemittedfromasolidobject-asemiconductororotherphoto-reactivematerial.
Unliketraditionallighting,SSLsourcescreatevisiblelightwithoutheatasacomponentoftheluminousemission.Thisdoesnotmeanthatheatisnotgenerated.
LEDsproduceasmuchheatasanysourceofasimilarefficiency.However,theheatfromanLEDiscontainedinthesemiconductormaterial,tobesinkedorextractedawayfromthevisiblelightemission.
Atthistime,thelargestissueinadaptingLEDstogeneralilluminationisthermalmanagement.Heathasaneffectonlightoutput,andcolor,andisthefocusofagreatdealofresearchinthismarket.Further,asefficienciesincrease,andmethodsaredevelopedtoextracttheheatfromthesemi-conductormaterials,theheatgeneratedbyLEDswillbelowerthanconventionalsourcesofsimilarlumenproduction.Theultimategoalistoreachefficiencieshighenoughtosubstantiallyreducetheissueofthermalmanagementinlightingproductdesigns.
Asageneralrule,solid-stateproductsexhibitgreaterresistancetoshock,vibration,andtemperatureextremes,therebyincreasingtheirpotentiallifespansignificantly.However,directcontactwiththeLEDsourcesthemselves(pressingontheirface,ordirectlystrikingthem)destroystheinternalstructureofthedevices,requiringtheybeprotectedinsomemanner.
SSLhasbeendescribedbytheUnitedStatesDepartmentofEnergyasapivotalemergingtechnologythatpromisestoalterlightinginthefuture.Itisthefirstnewlightingtechnologytoemergeinover40years,withthepotentialforenergyefficienciesandcostsavings,ispotentiallyaverydisruptivetechnologyinthemarketplace.
1.LEDHistory
For150yearslightingtechnologywasmainlylimitedtoincandescence,fluorescence,orarcdischarge.However,energyefficienciesoftheseconventionalsourceshaveessentiallyreachedapeakofroughly25%(75%ofenergyconsumedisheat),withincandescentlightingachievinganefficiencyoflessthan2%.WiththeadventofcommercialLEDsinthe1960s,however,adoortoanewandexcitingformoflightingtechnologywasopened.Fromthebeginning,researchersrealizedthatLEDshaveatheoreticalpotentialtoexceedtheefficiencyofconventionalsources.
Justastransistorsreplacedtubesinelectronics,solidstatecircuitsconsumelessenergythroughareductioninparasiticloss(heat)thatcannotberesolvedwithconventionalglasstubetechnologiescurrentlyprevalentinlighting.
InitiallyLEDswereredincolor,withgreen,yellow,andorangevariantsfollowingsoonthereafter.In1993,ShujiNakamuraofNichiaChemicalIndustriescameupwithablueLEDusinggalliumnitride(GaN).Withthisinvention,itwaspossibletocreatewhitelightwithanLED,openingtheopportunitytoputthesedevicestoworkingeneralillumination..
2.TechnologyOverview
(1)WhiteLightGeneration
AsingleLEDcanonlyproduceasinglecolor,specificallyred,green,blue,amber,oryellow.ToproducethewhitelightitisnecessarytoconvertlightfromanLEDtolightspanningthevisiblespectruminsomefashion.Toattainthis,threeapproachesareusedforgeneratingwhitelight:
Wavelengthconversion;
Colormixing;
andmostrecentlyHomoepitaxialZnSe.
WavelengthconversioninvolvesconvertingsomeoralloftheLED'
soutputintovisiblewavelengths.Methodsusedtoaccomplishthisfeatinclude:
(a)BlueLED&
yellowphosphor-Consideredtheleastexpensivemethodforproducingwhitelight.BluelightfromanLEDisusedtoexciteaphosphorwhichthenre-emitsyellowlight.Thisbalancedmixingofyellowandbluelightsresultsintheappearanceofwhitelight.
(b)BlueLED&
severalphosphor-Similartotheprocessinvolvedwithyellowphosphors,exceptthateachexcitedphosphorre-emitsadiferentcolor.Similarly,theresultinglightiscombinedwiththeoriginatingbluelighttocrea
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