背光资料PPT演示课件

IlluminationDesignForAutomotiveInteriorApplications,AdamZysnarski2002,ElectronicDesignSeminarSeries,BacklightingDesign,1,Outline,Thegeneralbacklightingproblem.,2,Outline,SpectrumandColorDefinitionofSpectrumHowisColordefined1931CIEChromaticityDiagram,3,Outline,PhotometryFluxSolidAngleIntensity,“Half-angle”IlluminanceLuminanceTransmittance/OpticalDensity“Practical”DefinitionsofTransmittanceTypicalSources,4,Outline,GeneralBacklightingRevisitedDirectBacklightingIndirect(Reflector)BacklightingIndirect(Lightpipe)Backlighting,5,Outline,NotesonBacklightingUsingLEDsPackagesBiasingThermalConsiderations,6,TheGeneralBacklightingProblem,A,A,A,7,TheGeneralBacklightingProblem,NeedtoQuantify:SourceLightQuantity,Directionality,ColorContent,PolarizationMediumThroughputGeometry,Reflectance,LightpipeEff.,PolarizationGraphicCharacteristicsTransmittance,Diffusion,Color“Filtering”,Polarization,8,SpectrumandColor,Energy=const/wavelength(JOULES)Power=Energy/time(WATTS)SpectrumisPOWER/WavelengthInterval,9,SpectrumandColor,DecomposesourcespectrumusingTristimulusFunctionstoobtainx,ycolorcoordinates,10,1931CIEChromaticityDiagram,11,Photometry,R,12,Photometry,LuminousIntensity,I=df/dW(SI:Candela,cd)Functionofangle,13,Photometry,Illuminance,E=df/dA(lm/m2)Amountoffluxperunitareacrossingasurface(fluxdensity),D,ForDsmallcomparedtod:E=I/d2,14,Photometry,Howdowetypicallyquantifythe“brightness”ofabacklitgraphic?,LUMINANCE,L=dI/dA(SI:cd/m2,English:footlambert,fL),15,Photometry,“Lambertian”Anemitter(orreflector)issaidtobeLambertianiftheluminancefromthesurfaceisconstantoverthehemisphere.,So:,16,Transmittance,PinandPoutrarelycollimatedPindistribution“source-like”Poutdistribution“diffuse”AbsorptionandreflectionalsooccursOpticaldensity,17,Transmittance,Matchtransmittancegeometrytoapplicationasappropriate:,18,Transmittance,19,DirectBacklighting,A“pure”greenLEDistobeusedtobacklightabuttongraphicofextentD=8mmatadistanceofd=18mm.Thegraphiciswhite(i.e.spectrallyflat)withatransmittanceinthegreenof7%.TheluminanceistargetedatL=3.4cd/m2(=1fL).Determinetheintensityandhalf-anglerequiredto“evenly”backlightthegraphic.,20,DirectBacklighting,Half-angle:Intensity:Onthebackofthegraphic:Onthefrontofthegraphic:,21,IndirectBacklighting(Reflector),Alightboxistobeconstructedtobacklighta14.6cmx4.9cmLCD.TheLCDtransmission(diffuseluminance)forLEDgreenis10.3%.Assuming100%throughput(I.e.perfectreflectingwallsandnolighttrapping)whatistheminimumnumberof40mlmgreenLEDsN,requiredifIwanttoachieve4cd/m2outoftheLCD?,22,IndirectBacklighting(Reflector),23,IndirectBacklighting(Lightpipe),Throughputofthesystemcanbeviewedasthesum:Canstillthinkintermsofthephotometricquantitiesalreadydefined:Needmoredescriptivephysics,24,LightRays,Travelinastraightlineuntiltheyencounterasurface.Twopolarizationcomponents,oneintheplaneofincidence,oneperpendiculartotheplaneofincidence.Initially,thelightraysusuallycontainequal“amounts”ofpolarization.,25,IndexofRefraction,Describestheopticalbehaviorofamaterial.Wavelengthdependent(“dispersion”).Complexnumber.Realpartspeedoflight.Imaginarypartattenuationofray.,26,TypicalValuesofn,Polycarbonate,l=550nmn=1.59-0.1iAcrylic,l=550nmn=1.49-0.01i(PlexiglassV825)Air(vacuum)n=1.0,27,When,rayenergywillreflect:Portionoftheraywillrefract:n1n2,Reflection,28,Amountoflightreflectedatinterface,R,isafunctionofangle,andcalculatedusingFresnelsequation.Perpendiculartointerface:ForAcrylic,i.e.4%oflightisreflectedbackinthedirectionofthesource.,FresnelReflectance,29,FresnelReflectanceForAcrylic,AverageforBothPolarization,30,Atthecriticalangle,alllightisreflected:Foracrylicinair:Canonlyoccurifn1n2.,TotalInternalReflectance(TIR),31,BendinglossesinLightpipes,R,t,MinimumRadius:,Forglassandacrylic:,ForLexanP.C.:,32,LightpipeTransmission,33,LightpipeSummary,Lightpipemusthaveahighernthansurrounding(ie.Airgapsare“good”whentryingtoreflectlight).Criticalangleshouldbemaintainedtoguidelight.Example:bendradius;radiusofbendshouldbemuchlargerthanthicknessoflightpipe.,34,Raytracing,LightTools(OpticalResearchAssociates,Pasadena,CA)isaMonteCarlosimulationraytrace.Capabilitiesincludecalculationsofflux,intensity,illuminance,andluminance.,35,Raytrace,36,NoteonLEDBiasing,Currentcontrolsluminance;forwardvoltageabovejunctionvoltageensurescurrentflow.,R,V,IF,VF,R=(V-VF)/IF,Intensityis“reasonably”linearwithIFfor“normal”ranges.,37,NoteonLEDBiasing,Forwardcurrentmustbe“derated”dependingonexpectedambienttemperatures,38,References,IntroductiontoRadiometryandPhotometry,W.R.McCluney,1994ArtechHouse.The