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DesignDesign

    Design

Designof25?_inchDirectIllumination’_typeLEDBacklight

    ;LIANGBao.wen,LIRongyu,GUOYingying,WANGShuai,CHENXiu-jin ;(StateKeyLaboratoryofLocalFiber-opticCommunicationNetworksandAdvancedOpti

    calCommunication

    ;Systems,DepartmentofElectronicEngineering,ShanghaiJiaotongUniversity,Shanghai

    200240,C)

    ;I

    ;Abstract..Weutilized”directillumination-type”LEDbacklightproject.madewhite—lig

    htLEDarrayin

    ;rectangle,designedasheetofreflectivefilm,asheetofdiffuserandtwosheetsofbrightnesse

    nhancement

    ;film,thenanalyzedilluminancechartwhichwastheresultofsimulationinseveraIdistance

    betweenreflective

    ;filmandopticalfilm.Itshowedthebestmatchingbetweenilluminanceanduniformitywtiil

    ein25mm

    ;distance.Finally,wediscussedsomeproblemswiththermaldispersion.

    ;Keywords:backlight;LED;directuniformity ;CLCnumber:TN31Documentcode:AArticleID:10070206(2008)030143;04

    ;1Introduction

    ;Now,mostofthelargearealiquidcrystaldisplay ;(LCD)displaysutilizecoldcath0defluorescents ;tube(CCFL)astheirbacklights,butCCFL

    ;backlightscouldonlyrecovernobetterthan8Oof ;thecolorwhichnationaltelevisionsystemcommittee ;(NTSOsignaliSabletotransmit:Asakindofnew ;illuminationtechnology,LEDhasmoresuperiorities ;thantraditionalbacklightinenergysaving,color ;improvementandrecover,andpicturequality[]as ;showninFig.1.

    ;Theadvantagesprovidehighercontrastand ;clearlyhierarchyfordisplay.Byusing6V;4OV

    ;Fig.1ComparisonofchromaticitydiagrambetweenLED ;andCCFL

    ;lowvoltagepower,thedesignofLEDpowersupply ;modulebecomesrathersimpleE.Usefultimeof ;LEDmaybelongenoughto100thousandhours, ;whichenormouslyprolongtheusefultimeofLCD. ;LEDbacklightisflexibleinmodulatingillumination ;frequencywhichisgreatlyhigherthanthatofFig.2

    ;CCFL,anditcouldperfectlyexhibitmovement ;LEDmodel[x(width)=5.5mm;(height)1

    ;mmandz(1ength)5mini

    ;pictures.AsthebacklightofLCD,LEDwouldmakebrightnessanduniformitymoreexcell

    ent.

    ;Forrawandprocessedmaterials,LED,whichisworthyofthenameofgreenenvironmentpr

    otection

    ;production,avoidstheexistenceofpollutionelements,i.e.plumbum,hydrargyrum;andis

    more

    ;convenienttorecycle.

    ;Receiveddate:20080513;reviseddate:200807l6

    ;?143?

    ;

    ;SemiconductorPhotonicsandTechnologyAug.2008 ;Fig.2sh.wsatype.fflakeLEDwithwhitelightweadoptedin.urexperiment?LEDwaspr.du

    ced

    ;byOSRAM,witharatedcurrent.f350mA,forwardVoltage.f3.2V,1umin.usintensity.f4O

    1m/w,

    ;andradiationangleof120degree.WechosewellmatchingLEDasourlightsource?

    ;2BigAreaLEDBacklightStructure

    ;Thecomn1onbacklightstructuresinclude ;“Direct’’and”Side’’illumination-typesfortheir

    ;differentcouplingmodes.In”Side”illumination:

    ;type,lightisincidentfromsidetolightguideplate,

    ;whichdiffuSesincidencelighttoplanarlight..In ;“Direct’’illumination-type,lightisincidentfrom

    ;bottomanddiffusestoplanarlightbyDiffuser. ;Figs.3and4are”Direct”and”Side”illumination—

    ;typessketchmaps.

    ;Weadopted”Direct”illumination;type,whose

    ;simulationsketchmapisshownasFig.5,fromtop ;tobottomarebrightnessenhancementfilm(BEF)

    ;(firstfloor),BEF(secondfloor),diffuser,andthe ;reflectivefilm.

    ;Firstly,lightradiatedfromsourceswouldpass ;throughdiffuserandtransformtopreferable ;uniformitylight[,thenthroughtwosheetsof

    ;brightnessenhancementfilmswhichcouldenhance ;thebrightnessofegation

    ;LEDalTa3

    ;“Direct”illumination-type(Filml:diffuser;

    ;Film2:brightnessenhancementfilm;Film3: ;reflectivefilmandFilm4:lightguides)

    ;ofreflectivefilminthebottomofLEDmatrixandfourrefl

;.

    ;ectivewallsaroundit,whichcouldenhance

    ;efficiencyandbrightnessoflightsourcesineffect,increaseabout1O%ofedgebrightnessandgainbetter

    ;uniformity.

    ;Nowweintroducethefunctionandmaterialofeachfilm:

    ;(1)Diffuser,withhighHaze,hasstrongdispersioneffectonlight,.hazetheincidentlightby ;refractionandreflectionofdiffusematerial,centralizelighttothefrontbysmallangle,andenhance

    ;1uminance,a11ofwhichleadtopreferableuniformitylight.Inthispaper,weutilizedatypeofdiffuser

    ;withonehazesurfaceandtheotherbrightsurface,0.1mmthickness.85Haze.ForDiffuser,we

    ;sDreadtransparencebasestuffwithdiffusematerial,whichleadsthetransmissionlighttodiffusionand

    ;uniformity.AndimprovedisHazeeffectively(especia11yforalittlemorethickDiffuser)intheproduct

    ;withbrightness-enhancementfilmscombination.NowweintroduceHazecomputationbriefly:

    ;Hazedfeinition:Hazerepresentthediffusiondegreeofincidencelight ;一壤/,~D…iffuselight\Dise1ight

    ;Totallytransmissionlight=parallellight+diffuselight

    ;Haze=

    ;(2)BEF:prismsarrayinparallel

    ;?

    ;144?

    ;diffuselight

    ;totallytransmissionlight

    ;initssurface,its

    ;×lo0%

    ;opticalprinciplepictureisshowninFig.6.By

    ;

    ;V0l_14NO.3LIANGBW,eta1.Designof25

    inchDirectIllumination-typeLEDBacklight

    ;utilizingthetota1reflectionofprismwithrightangle,BEFletsdispersivelightcentralize

    ontherangeof

    ;7Odegreenormaltoemission.Namely,dispersivelightinalldirectionsconcentratesonasmallerrange

    ;bvBEF,whichincreases40;

    7O9/5Ofbrightnessonthatrange.Inthispaper,weusedtwoBEFS

    ;whoseDrismdirectionwasverticalmutually,inthiswaybeamcentralizedinconicalangleofview

    ;eauabIv.Thethicknessofeachfilmwas0.03mm,andthemateria1wasopticalglassBK7. ;(3)Reflectivefilm:inthispaper,thethicknessofreflectivefilmwas0.01mm,materialwas

;aluminiumD1atewithgoodperformanceofheatdissipation,anditsreflectivitywas98.

    ;Fig.5”Direct”illumination—typesimulationsketchmap

    ;3SimulationResultandAnalysis

    ;Wedesigneda25inchbacklight,therationof

    ;longsidetoshortsideofrectanglewas16:9,

    ;whichwasprevalentpresently,andthealtitude

    ;ofreflectivefilmtothefirstBEF(ARB,RB)

    ;was25mm.LEDsmatrixweutilizedcontained

    286LEDswhosedistancebetween ;22X13

    ;everytwoLEDswas25mm.Thesimulation

    ;illuminancematrixsimulatedbysoftwareof

    ;lighttoolsisinFig.7,andyisthesidelength

    ;ofbacklightplaterespectively,andthevaluesin

    ;chartcorrespondtoilluminance(unit:Lux).

    ;Fig.6Brightnessenhancementfilmstructureschematic

    ;diagram

    ;Fig.7Illuminanceanduniformitychartofbacklightwith286 ;LEDsof25mmspacing

    ;Moreover,inordertoexplaintherelationofLEDspacedistanceandARBin-depth,wemade

    aseries

    ;ofsimulation,theresultsareshowninTabs.1,2,3(unit:Lux): ;Thecacu-ati.nrmu-a.runirmityis:unirmity===篆亲xlooG

    ;Tab.1Relationof/’ARB,illuminanceanduniformitywhenspacedistanceofLEDsis20m

    m

    ;1ARB/mm15202530

    ;Illumanance/lux58000/7000056000/6600053000/64O0052000/63000 ;(Min,/Max)

    ;Uniformity82.8684.8582.8282.54

    ;Tab.2Relationof.

    ;RB,illuminanceanduniformitywhenspacedistanceofLEDsis25mm ;PaRB/Fain152O2530

    ;Illumanance/lux40000/5000038000/4600038000/4300035000/42000 ;(Min/Max)

    ;iUniformity8O82.6188.3783.33

    ;?

    ;145?

    ;

    ;SemiconductorPhotonicsandTechnologyAug.2008

    ;Tab.3RelationofnRB,illuminanceanduniformitywhenspacedistanceofLEDsis30mm

    ;rARB15202530

    ;Illumanance/lux29000/3900027000/3600026000/3400023000/31000 ;(Min/Max)

    ;Uniformity74.367576.4774.19

    ;Tabs.1,2,3aretherelationsofI1ARB,illuminanceanduniformitywhenspacedistanceofL

E:Dsis20

    ;mm,25mm,30mmrespectively,thetotalnumberofLEDsis448,286,209,respectively.Thetables

    ;show:

    ;(1)WhenthespacedistanceofLEDsisfixed,theilluminanceisloweralongwithhigherrARH,but

    ;higheralongwithlowerFgpx.ItismainlyinrespectthattheluminousfluxemittedbyLEDsisfixed

    ;becausethenumberofLEDsisfixed,wellthenhigher/’ARBleadslessluminousfluxtoarriveatreceive

    ;surface(whichisonthetopofthefirstBEF),therefore,lowerilluminance. ;(2)WhenFgRBisfixed,illuminanceisloweralongwithlongerspacedistanceofLEDs;illuminanceis

    ;higheralongwithshorterspacedistanceofLEDs.ItismainlyinrespectthatonconditionoffixedI1ARB,

    ;moredenseLEDs,more1uminousfluxwithinthisrange,therefore,higherilluminance. ;(3)But,theuniformityisusuallynon-monotonicity,nootherthansimulationinavarietyof ;conditionscouldgainthebestresult.InTabs.1and2,whenthespacedistanceofLEDsapproaches

    ;-PARB,theuniformityisbestofal1;inTab.3,al1thevaluesofuniformityarenotverywel1,duetothe

    ;sparsearrayofLEDs.

    ;Designresult.inTab.1,uniformityispreferablein20mmARB,withhigherilluminance,however,

    ;ifwedesignasTab.1,thetotalnumberofLEDsis448,whichincreasethetota1powergreatlyin

    ;practice.Actually,RBisinvolvedinthermaldissipation,20mmaltitudeisbetterintherma1dissipation

    ;than25mmand30mm.InTab.3,alltheilluminanceanduniformityarelow,becauseofthesDarse

    ;arrayofLEDs.InTab.2,whenspacedistanceofLEDsis25mmandPgRBis25mm,uniformityand

    ;illuminanceareuptothebestmatching,whichisjusttheconfigurationweadoptedinthispaper.

    ;Inthecaseofthermaldissipation,whenhighpowerLEDsworkinratedcurrent,theyaree

    mittinga

    ;largeamountofheatenergy,easytogeneratehightemperature.Unlessdissipateheatintime,itisquite

    ;easytobreaktheequipment.Therefore,weusedaluminiumplateasreflectivefilm,andledupperLEDs

    ;tobetterthermaldissipation.

    ;WecouldalsoconnectthermaldissipationpatchtoPCB,andenhance

    ;thermalarea,whichhelpstoresolvehightemperaturematter..

    ;4Conclusion

;Wedesigneda25

    inchdirectillumination-typeLEDbacklightandanalysedthesimulationresuits ;.The

    ;con?igurationis:ratedcurrentis350mA,forwardvoltageis3.

    ;2V,luminousintensitvis4O1m/W,and

    ;adiationangleis120degree.Fromtheanalysisabove,whenspacedistanceofLEDsis25mmandP

    ;gRB

    ;1S25mm,wecanget40000Luxilluminance,88.37uniformitybacklightsyStem,andthistypeof

    ;designcouldsatisfytherequirementofTFTLCDDane1.

    ;References:

    ;[1]WANGMin,XIAXian_jun.TechnologYandapplicationsofthenewLEDbacMight[J]. ;Optoe1ectronicTechno1ogy,

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    ;Biography:

    ;LIANGBnown(1981),male,anativeofLiaoningprovince,China.Heisstudying ;inShanghaiJiaotongUniversityforM.S.degree.Hisresearchinterestisinthefieldof ;LCDbacklightdesign.

    ;Email:buyongmima@sjtu.edu.ci1

    ;(Continuedfro,~page178)

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