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1、IEEEJOURNALONSELECTEDTOPICSINQUANTUMELECTRONICS,VOL.8,NO.2,MARCH/APRIL2002333Red,Green,andBlueLEDsforWhiteLightIlluminationSubramanianMuthu,AssociateMember,IEEE,FrankJ.P.Schuurmans,andMichael.D.PashleyAbstract—Therapidimprovementofthewhitelightefficacyach
2、ievablewithlight-emittingdiodes(LEDs)opensupnewoppor-tunitiesinthegeneralilluminationmarket.AnLEDlightsourcemadeofred,green,andblueLEDs(RGB-LEDs)canprovidetheuniquefeatureofcolorvariability,allowingtheusertoselectthedesiredcolorpointofthelamp.Thewhiteligh
3、tcoloraccuracyre-quiredinthegeneralilluminationmarketisachallengeforLEDs.Thevariationinlumenoutputandwavelengthfornominallyiden-ticalLEDsandthechangeintheseparameterswithtemperatureandtimeresultinanunacceptablyhighvariabilityinthecolorpointofwhitelightfro
4、mRGB-LEDs.Inthispaper,weshowthattheseproblemscanbeovercomewithsuitablefeedbackcontrolschemesthatcanbeimplementedinapracticalLEDlamp.Wepresentresultsofexperimentandtheo-reticalmodelingthatshowstheperformancethatcanbeachievedwithanumberofdifferentcontrolsch
5、emes.IndexTerms—Coloraccuracy,feedbackcontrol,light-emittingFig.1.The1964CIE(u;v)coordinatesystemshowingthecoordinatesofdiodes,whitelightillumination.InGaNandAlInGaPLEDs.Alsoshownistheblackbodylineoverarangeofcolortemperaturesfrom2000Kto10000K.I.INTRODUCT
6、IONAkeychallengeforRGB-LEDsistomaintainthedesiredwhitepointwithinacceptabletolerances.Thisarisesfromthesignif-HERAPIDdevelopmentoflight-emittingdiodes(LEDs)icantspreadinlumenoutputandwavelengthofmanufacturedToverthelastfewyearshasopenedupnewopportunitiesi
7、nLEDs,andthechangesinLEDcharacteristicsthatoccurwiththegeneralilluminationmarket[1].Theefficacyofwhitelighttemperatureandtime.MaintainingthedesiredwhitepointcanfromLEDsisnowover20lm/W,whichalreadyexceedsthatonlybeachievedwithfeedbackschemestocontroltherel
8、ativeofincandescentlamps[2].By2005,itisforecastthatLEDef-contributionsofred,green,andbluetothewhitelight.ficacywillreach50lm/W[3],whichapproachesthatofcom-pactfluorescentlamps.Inaddition,higherpowerpackagesareII.WHI
