Uniform white light distribution with low loss from coloured LEDs … · 2019-12-13 · Uniform...

Uniform white light distribution with low loss from coloured LEDsusing polymer doped polymer mixing rods

Chris A Deller Geoff B Smith Jim B FranklinDept Applied Physics University of Technology Sydney

PO Box 123 Broadway 2007 Australia

ABSTRACT

Colour mixing of red green and blue (RGB) LEOs is demonstrated for a 6 em long PrvLv1Acylindrical rod with atransparent refractive index matched micro particle (TRIMM) diffuser sheet at the output end Ray tracing simulationshave been performed and the output light distributions transmittances and losses modelled and compared withexperiment Photographed and modelled colour mixing results are presented for rods with and without TRIMM sheetmixers The TRIM~f particles homogenize the light output of plain Pf~fA rods to form white light with negligiblebackscattering A simple method for measuring the concentration of the particles in the diffuser sheet is described andcomputer modeling and analysis of TRIMM particle systems is discussed

1 INTRODUCTION

Mixing rods are used to homogenize light output from multiple sources in devices such as backlit liquid crystal displaysand data projectors Designers want high efficiency and output uniformity in minimum possible size It has been statedthat a length to width ratio of about 10 I is required to achieve the necessary output light uniformity Shorter lengths aredesirable as the size of devices is steadily decreasing

Mixing rods that rely entirely on total internal retlection (TIR) such as plain PMlvLltrods have the disadvantage thatundesirable patterns are produced due to caustic effects It has been reported in a previous study of RGB colour mixingthat clear PMfA mixing rods made no significant improvement in illuminance or colour uniformity compared to a bareLED array A diffuser at the output end significantly improved the output light distribution but with an additional loss of62 Transparent refractive index matched micro (TRIivIM) particle mixers homogenize the light output with low lossbecause the microsphere particles deviate the light rays by a small amount each interaction with low backscatter

The diffuser sheet used in this experiment consists of cross-linked P~flvL- spheres (TRIMM particles) embedded in aPlN1A matrix The mean particle size is - 35 llJ11 in diameter A study of the optical properties of similar sheets hasbeen published Light transport in polymer optical fibre doped with TRIMM spheres has been reported and a papershowing uniform colour mixing ofRGB light sources using PMMA extruded rods containing TRLvIM particles willappear soon In this study we incorporated TRINLvl particles into the light mixer system in a diffuser sheet at the outputend of a clear PMMA rod There were several reasons tor this approach Firstly the extruded rods studied previouslywere not of sufficient optical quality to experimentally ascertain any losses due to the TRIMM particles alone Inaddition the diameter of the rods was too small to use 5mm LED triads as light sources (Extruded larger diameter rodswere not available) It is also of interest to see how these particles perform as end diffusers instead of having TRIMMdispersed evenly throughout the rods

2 EXPERIMENT

Two transparent PfMA rods 2555 mm in diameter were used in this experiment A 294 mm thick TRIMM diffusersheet was glued to an end of a 5895 mm long rod using Loctite INIPRUV~ 34931 glue No air bubbles or defects werevisible at the interface which is indicative of a good optical joint Thus the total length of the rod with TRIMM sheetdiffuser is 598 mm The plain PMIvlA rod (referred to as clear) is 619 mm long

Fourth International Conference on Solid State Lighting edited by Ian 1 FergusonNadarajah Narendran Steven P Den Baars John C Carrano Proc oi SPIE Vol 5530(SPIE Bellingham WA 2004) 0277-786X104$15 doi 10111712556282

231

The sources that are mixed are two sets of 5 mm RGB LEOs denoted as Alpha group and Beta group Each groupconsists of a triad of 3 LEOS It is desirable for the individual angular source distributions within a set to be as similar aspossible The LEOs were selected from a larger pool of 5 mm LEOs all of which had been measured using aphotogoniometer described elsewhere A cross-section of the angular intensity distribution of the Alpha and Beta groupLEOs as measured by the photogoniorneter is shown in Figure I Spectra of the LEOs were obtained via an OceanOptics S02000 tiber optic spectrometer coupled to an Oriel 70491 integrating sphere and associated software 1931 CIEcoordinates for the LEOs were derived from the respective spectral power distributions These source CIE coordinatesand the LED peak spectral wavelengths are given in Table 1

b) Beta Group1------ -- ---

I

a) Alpha Group

-- Redi-Green Blue

40

I

II--

~~I r ~

bull tobullbullbullbull

-- Red

- Gr e e n Blue I

--40 -20J 20

Angle from Normal 1deg)

--40 -21) 0 LIJ

Angle from Normal deg140

Figure 1 Measured angular distribution of the source LEOs a) Alpha group b) Beta group

Alpha Group CIE x CIEy Beta Group CIE x CIE y

Alpha Red (642nm) 0701 0294 Beta Red (632nm) 0691 0301

Alpha Green (509nm) 0114 0681 Beta Green (513nm) 0162 0674

Alpha Blue (462nm) 0135 0058 Beta Blue (460nm) 0138 0062

Table 1 1931 CIE coordinates and peak wavelength of the source LEOs as measured using a spectrometer

The Alpha group LEOs are better matched in angle than the Beta group but the Beta group is superior in terms of colourfor RGB mixing as the spectra of the Beta peaks are more widely spread (The spectral peaks of Alpha green and blueare closer together (Table I )) For the computer modeling a separate source model was generated for each LED based onthese measured profiles

The experimental setup for measurements is shown in Figure 2a The Alpha or Beta RGB LED triad was mounted asclose as possible to the end of the mixing rod The centre point of the LED array was aligned with the rods axis Afrosted glass screen (dimensions 120 mm x 955 mm) was positioned 4 ern or 15 ern from the exit end of the rodPhotographs of the transmitted output distributions were taken with an Olympus C-4000 ZOOM digital cameraTransmittance measurements were performed using the Alpha LED source array and the clear and clear + TRIMMdiffuser rods with the output end coupled to the entrance port of an Oriel 70491 integrating sphere A BPW21photodiode was attached to the detector port of the integrating sphere and readings taken with a Data Precision OP 100Multimeter The ratio of the transmitted to incident readings were taken using measurements of the bare LED array asthe total incident light

232 Proc of SPIE Vol 5530

a) c)

o 2S IIIl1 pigtola

Figure 2 a) experimental setup LED array mixing rod frosted glass screen b) photograph of Beta LEOs and clearPMrvlA rod - 20 ern from the rod exit surface at an off-axis angle to avoid excessive over-exposure TIR from the rodsurfaces is visible c) modelled clear rod exit end surface illumination of modelled Beta LEOs

3 TRIlIl1PARTICLES AND MODELING

Ray tracing simulations using 1 million initial rays for each source LED were carried out to model the experimentalconditions The rays were emitted uniformly over a -1- mm diameter area and measurement-based algorithms were usedto realistically simulate the LED light output Output rays from the end of a rod are traced to modelled screens atpredefined distances from the rod exit end The number of rays that hit each pixel in each modelled screen is recorded Aseparate simulation was carried out for each LED and the RGB results combined for the simulated output intensity andcolour distribution Details and relevant colour calculations have been reported recently Transmittance and loss data ismodelled by counting the number of rays exiting or reflecting from the relevant rod surfaces

The Monte Carlo ray tracing modeling within a light guide has previously been described elsewhere The basic conceptsare reviewed in Figure 3

a)

- J ~ampgt)~~h_ -I--~8---

) I

b)h = Hrm = n] n

=l+fl

oz H

8 = 2[sin-I (h) - sin (him)]

Figure 3 a) Defining ray direction as it propagates along a TRI~lil mixing rod b) Angular deviation of a ray when itstrikes a TRIMM sphere Note that 8is in 3 dimensions involving a change in both e and cent

The direction of propagation of a ray along a mixing rod is described by the angle e with the light guide axis z andthe azimuth angle f1 as shown in Fig lao Every time a ray strikes a TRIM~l particle there is an angular deviation ~shown in Fig Ib The ratio h used in the calculation of deviation angle is chosen randomly for each interaction of a raywith a TRIMM sphere to give uniform probability of impact point The deviation can be described in terms of geometricoptics because the size of the particle is large compared to the wavelength New eand centdirections for the deviated rayare calculated using 3D spherical geometry after each particle interaction

Proc of SPIE Vol 5530 233

The relative refractive index m = nrphaenmltllrir can be usefully described by its difference from one m = 1+fI In TRIMMsystems fJlaquo 01 so the deviation angle is small and back reflectance is gt 4 which is negligible In addition smallchanges in nmltllrIX or ngtphere can cause large changes in J1 and thus the scattering properties of the system The deviationof a light ray after encountering a TRIMM sphere has been given by

(1)

The simpli tied approximation 2jJh -( I_h2) is derived using a Taylor expansion of (l +u) and neglecting higher order

terms The median value of h the radial fraction of contact of a ray with a sphere is l~ Substituting this into Equation(1) the median deviation angle 4 is thus

~m = 21

Foru= 001 L Sn = lJ and foru= 00184 = 21deg

(2)

The effect of changing m (and thereforeu) has on the distribution of deviation angles is shown in Figure 4 Figure 4ahas u for TRIM~1 particles in PMrviA (n = 1490 nJ = 1507u= 0011 at 590 nm) It can be seen that most deviationsare -1 or 2 degrees Figure 4b shows the distribution for TRIMM particles in POF matrix as previously described (n= 1480 u = 0018 at 590 nm)

Devi ol1iom =gle of nyoIfter hi 11iTl9 01 mi e rOJphe n

Deviol1iom =gle of rolYoIf1er hi 1tiTl9 01 mi e rOJphe re

t5000

15000tOOOo

~ 15000

~ 10000~

~ubullbull~

H500gt-~ 10000

~ 1500bullbull~ 5000

t5005000

1 t 3 4 5 6 1 8 9 10 lilt 13 14 15Devi oItiom (de gn e J )

a) m = 1011 2u= 13deg

1 t 1 4 5 6 1 8 9 10 lilt 13 14 15Devi oI1iom (de gree J )

b) m= 1018 2fJ=2Io

Figure 4 Frequency of deviation angles upon encountering a TRIMM particle for m = 1011 m = 1018

sect~ubullbull~

31 Determination of TRIMM particle concentration in sheet

The number of particles encountered by a light ray along its path through a TRI~fM mixer is related to the volumeconcentration of the particles in the matrix For purposes of Monte Carlo computer ray tracing we need to know themean distance between particles I This was not known for the diffuser sheets used and had to be measured We definethe axial particle number a of a diffuser sheet as the average number of particles that an undeviated ray wouldencounter when passing through the sample For a sample of thickness t I = ta So by measuring a I can bedetermined

The probability of an undeviated ray striking a particle as it passes through a sample can be described by a Poissondistribution

-(J x

p(x)= e a forx=012 x


(3)

where o is the average number of events The probability of a ray striking zero number of particles when travelingthrough a sample with axial particle number a is

(4)

where Tpec is the specular transmittance

32 Measurement of axial particle numberMeasurement of the true specular transmittance of a particular sample can be used to estimate a In order to do this theaxial particle number of a particular sample must be small enough to ensure a visible specular component For a = 6Tpec is 00025 The concentration of TRIMM particles in the diffuser sheet used is sufficiently high to necessitatemeasuring thin slices laquo 1 mrn) so slices were cut from the main sheet using a diamond saw To ensure optically smoothsurfaces for measurement these slices were mounted between sheets of2 mm thick PMlv1A using glycerol between eachof the surfaces as a refractive index matching agent

A helium neon laser (wavelength 633 nm) was used for the transmittance measurements that were used to calculate a Anadvantage of using a laser is the relative ease of being able to see an transmitted undeviated specular spot indicatingthat the samples are sufficiently thin for axial particle measurements as well as making alignment easier An Oriel 70491integrating sphere was positioned 38 m from the sample and readings taken using a BPW21 photodiode at the detectorport and a multimeter with a resolution of 1 JlWTo estimate a it is necessary to separate the specular component oftransmission from the diffuse The port size of the integrating sphere was reduced to 1 ern diameter with a cover makingthe acceptance criterion for specular transmission within a cone semi-angle of 0075 degrees The laser beam wasdirected through the sample towards the integrating sphere The component of measured transmittance in the incidentbeam direction Imax was measured with the port of the integrating sphere in line with the undeviated beam This ismainly the specular part of the transmitted beam but also contains a small scattered cornpcnentLj This was subtractedfrom Imax to obtain the specular component of measured intensity The scattering baseline (middotCGII was estimated by movingthe integrating sphere I 2 and 3 ern to either side of the central axis corresponding to median angular deviations of-015 030 and 045 degrees and taking intensity readings The initial intensity 10was measured by directing the laserbeam into the integrating sphere through the PMMA and glycerol only The specular transmittance of the beam throughthe sample was then calculated by

(1 -1)T max call

spec 10

(5)

Three sets of measurements were made using slices of sheet 025027 and 033 mm thick to derive the linear particleconcentration of TRIMM in the diffuser sheet A was calculated for each sample using equation (4) and from this thedistance between particles was calculated to be 0075 to005 mm The TRIMM diffuser sheet thickness is 294 mmgiving an axial particle number of 39 plusmn3 for this experiment

33 Ray diffusion and angular spread with TRIMMA rays path along a TRlM~l mixer as it deviates with every sphere interaction can be described as a random walk Thehalf cone angular spread (I) of the light in the cross-sectional (x-y) plane as it proceeds internally through a TRIMMdoped material is dependent on the average deviation and axial particle number

(6)

For the TRIMM diffuser sheet used here I 130( ~9) = 810

bull This corresponds to an external half cone spread of 1210 after refraction upon exiting the guide end It should be remembered that this spread is in addition to theexisting spread inherent in the distribution of the source LEOs and that the clear rod partially mixes before the sheet

Sometimes the value of JI cannot be altered because it is set by the materials used In such cases axial particle numberand rod aspect ratio can be tailored so that total deviation I will cause the resulting cone of light to spread across theentire end of the mixing rod before exit This ensures completely homogeneous mixing with no caustics formed


34 Rotational symmetry and statistical analysis

Caustics are often formed when light mixing is performed relying on TIR only using clear undoped PMMA rods Thesecan be removed by adding a TRIMM diffuser to the end of a clear rod or having TRIMM dispersed within the mixingrod There may be cases where it is desirable to keep the TRIMM concentration low to avoid side loss say if u is largemeaning 8m will be larger (equation (2) and Figure 4) High angular spread of the source distribution can be anotherreason for keeping the TRIMM particle concentration as low as possible The chief geometrical factors affecting thedegree of caustics formation in a clear rod apart from the source distribution are 1) rod length to diameter aspect ratio(AR) and 2) the relative radial source distance of the LEDs from the rod axis (source radial fraction see Figure Sa)Computer modeling is useful for optimizing these factors to minimize caustics formed purely due to system geometryand for determining the optimal TRIMM concentration needed to homogenize the light output

For the computer modeling of colour mixing at least 3 sets of data one for each LED is generated for a particularsimulated screen to rod distance The 3 data sets are added together to form a complete colour maps If the modelledmixing rod output intensity from a single LED projected onto a simulated screen is not rotationally symmetric then thefinal colour mixing will be uneven Statistical analysis of modelled data can show how rotationally symmetric theprojected output intensity will be This gives an indication of whether bright caustics will be formed in an undoped rodand if TRIMlYl concentration is sufficient to cause complete and uniform colour mixing in a TRIMM mixing rod Thistype of analysis also aids in system design as AR and source radial fraction can be optimized to give uniform lightdistribution for a given Ji and TRIvllvl concentration

Modelled rays exiting a mixing rod for a single LED are projected onto a pixellated screen The value of each pixelcontains a number corresponding to the number of times it has been struck by an output ray This data is used to performrotational symmetry statistical analysis Figure 5 shows the concept of arranging the pixels into bins of equal radialintervals from the centre of the simulated screen The average number of rays per pixel and the standard deviation iscalculated for each radial bin This data plotted against the radial distance from the centre of the screen is a goodmeasure of the rotational symmetry of the light output

Radial distancefrom centre

r Radial bins

Source Radial Fraction= radial LED distance I Rrod

C Simulated screen divided into pixels

Figure 5 a) Schematic showing entrance end of mixing rod with relative positions of the LEOs to the rod axis (centre)and rod radius b) Pixels in a simulated screen are sorted into radial bins for analysis of rotational symmetry of outputlight distribution

4 RESULTS

41 Colour Mixing Results

Modelled and photographed results of the output light from the Alpha group LED triad projected onto a screen 15 emfrom the end of the mixing rods are shown in Figure 6 and 7 Figure 6 shows the colour distribution when using theclear PNllv1A rod only as the mixer Figure 7 shows the distribution from the rod with TRIMM diffuser sheet


a) b)

~) d)x

Colour erE x20 40 60 30 100 1~0

Colour CIE I20 40 60 80 100 120

20 ~O 60 80 100lIIlll

iiI

120

41 I~ 05

lmiddot

~ ~ 04 bullbullo Imiddot j8031 bullbull I~~ bull I - bullbullbullbullA bullbull 0 I liir e ~- bull t I

bullbull I fmiddotlf bulls 20 40 60 80

IIIIIl

Figure 6 ab) Output colour distribution transmitted through the frosted glass screen 15cm from the end of the clearPMMA rod a) modelled b) photographedcd) Modelled CIE coordinates of a horizontal strip through the centre of the screen c) ClE x d) CIE Y

a) b)-- W

o

~ ~-

c) d)

Colour CIE x

20 40 60 80 100 120Colour CIE Y

20 40 60 80 100 120

bullbull o 55 o j

omiddot 8 I) 3 bullbullbull bullbull bullbull bull bull bull bullbull- I bull bullbull - bullbullbullbull - A 1_ ~ (j 1 - bull~ ~~ - bullbull~ C Ibullbullbull I

~ vl Io Ibullfi 20 40 60 80 100 120

bullbullbullbull

05

~ 04g bullbullbull bull bull bull j

uO3 etl bullbullbull -- bullbull gt bullbull - -4~ ebullbullbull ~~ r- bullbull _bullbull --40 bullbull bullbullbull ~ Im 01 Iowcltgt 20 40 60 80 100 120

11III

Figure 7 ab) Output colour distribution transmitted through the frosted glass screen 15cm from the end of the clearPMMA rod a) modelled b) photographed cd) Modelled ClE coordinates of a horizontal strip through the centre of thescreen c) CIE x d) ClE y


The photographed and modelled images are both 120 mm x 955 mm Each pixel in the modelled screens representsI mm Excellent quantitative agreement between the measured and modelled CIE x and y coordinates derived fromcolour output from mixing rods and from corresponding modelled colour output has been demonstrated in a recentstudy CIE coordinates from modelled results only are shown here

An artefact of the photographs is the inability to display colour over a large brightness range The colours on the outerperiphery of Figure 6b actually appear brighter when viewed with the eye Similarly the blue halo in Figure 7b althoughslightly visible in the experimental system appears much lighter to the eye In addition it was difficult to generate asufficiently high intensity from the green LED to achieve a desirable colour balance as is evident in both the modelledand photographed results It can be seen however that a uniform colour is obtained across the screen because asFigures 7 c and d indicate the CIE plots of the rod + diffuser sheet results are constant

42 Transmittance amp LossesThe fate of rays can be categorized as detailed in Figure 8 in terms of key surfaces and ray directions at the surfaceResults are given for measured and modelled mixing of the Alpha LED array with clear 6 ern rod and for PMMA rodwith TRIMM mixer A- refers to the fraction of rays incident on the entrance end of the rod that are Fresnel reflected B-is the fraction of incident light (10) reflected from the end surface which is lost most of which is transmitted outthrough the source end of the mixer C + is the percentage of Itransmitted out of the end surface Light transmitted outof the side edges of the diffuser TRIMM sheet in any direction is given by D (For a clear rod D is negligible)

Transmittance measurements made for the individual red green and blue LEOs were averaged and compared withsimilarly averaged transmittances obtained from simulation data The results are shown in Table 2 The measured outputfrom the TRIMM sides (D) was obtained by difference by taking readings with the diffuser in and out of the integrating

IDI

---_+Figure 8 Schematic of mixer rod showing surfaces for which a transmittance or retlected loss is shown in Table 2

Clear PtjUA rod Clear rod + TRlJUJJ diffuser

Simulated Measured Simulated Measured

Imput Fresnel reflection losses A- 57 - 57 -Output end Fresnel losses B- 47 - 60 -~------------------------- --------- ------------- ------------- ------------- -------------

Forward useful output C+ 896 87 839 83

Lateral useful output D NA NA 44 60

Table 2 Simulated and measured Transmittance and loss results as a percentage of the incident light for Alpha groupLEOs for 6cm PMMA mixing rod with and without TRIMM diffuser measurement has higher uncertainty (see text)


sphere The measured transmitted end light for the rod + TRIMM mixer has a higher uncertainty than the othermeasurements This is because measurements using integrating spheres can only be accurately compared when theangular spread of the light is comparable The TRIMM diffusers used here produce an additional half-cone angularspread of about 20 compared to the clear rods (equation (6)) so a correction factor was estimated to account for theeffect that this difference has on readings obtained using the integrating sphere This correction factor was obtained bymaking measurements of the transmitted light from the LED array through a diffuser sheet alone compared withestimates based on previous measurements with two spectrophometers using a narrow collimated beam

43 Rotational symmetryThe average number of rays per pixel for each radial bin is plotted against the radial distance from the centre of amodelled screen in Figure 9a The screen was modelled at 15 em away from the end of the clear rod for the Alpha redLED If3 matrices of different colour are to be mixed there must be no sudden spikes or variations in the intensity ofthe individual LED outputs with screen radius for uniform colour mixing to be obtained Figure 9b shows the standarddeviation divided by the average rays per pixel for the same data as Figure 9a The expected values are those expectedpurely due to statistical fluctuations within the data due to the finite number of rays traced It is evident that the lightdistribution is not uniform across the screen and that if colour mixing were attempted with distributions such as thesecaustics would be formed Figure 9c amp d show the analysis of the same system modelled through the rod with TRIMMdiffuser sheet It can be seen that the light distribution has been smoothed and caustics will not result in this case

b)a)Average rays per pixel in radialbin vs radius from the centre of screen Std devAv rays per pixel for radial bin

vs radius from the centre of screen

(mm)

o 8- =============----- bullbullbullbull----bull modelled expected

Figure 9 ab) analysis of simulated ray tracing data projected onto a screen 15cm from the end of the 6cm clear PMMArod with Alpha Red LED as the source a) Average rays per pixel in a radial bin vs radial distance from the centre ofthe screen (see Figure 5b) b) std deviationaverage rays per pixel in a radial bin vs radial distance from screen centrecd) similar analysis for PMMA rod with TRIMM diffuser Outlying point in modelled data due to very small number ofrays hitting screen edge

2004ltII 150 - bulllt-rl0 100middotgtlt1l0

50

bull bullbullbullbullbullbullbullbull 04bull 02 bull bull t bullbullbullbullbullbullbull bull

0 _

o 0 20 30 40 50 60Radial distan~e from centre of screen (~mi

bullbullbullbullbullbullbullbull10 20 30 40 50 60

Distance from centre of simulated screen (mm)C)

Average rays per pixel in radialbin vs radius from the centre of screen

d)

Std devAv rays per pixel for radial binvs radius from the centre of screen

-a-bull bull bull 028

026024

bull modelled expected

40 bull bull4

~ 35--0- 30middotrJJ gt

~ 25

bull bullbull bull bull 022 Att-

02 i t 018 bullbullbull A1

i bullbull -

016 ~~ t bullbull__bull__ ~a 10 20 30 40 50 60

Radial distance from centre of screen

bull bull bull bull bull bull20 bull

10 20 30 40 50 60Distance from centre of simulated screen (mm)


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Volume 5530 Fourth International Conference on Solid State LightingChairslEditors Ian T Ferguson Nadarajah Narendran Steven P DenBaars John CCarranoConference CommitteeIntroduction

lEWAccelerating the development of next-generation solid-state lighting sources [5530-1]1 Brodrick C ChristyOverview present status and future prospect of system and design in white LEDlighting technologies[5530-3]T TaguchiTriple-doped white organic light-emitting devices grown in vacuum [5530-50]B DAndrade R Holmes S Forrest J Li M Thompson

Al)PIJCATIONSAn examination of a prototype LED fire-alarm signaling appliance [5530-4]1 Curran S Keeney

IDevice performance of AlGaN-based 24o-300-nm deep UV LEDs [5530-5]A Fischer A Allerman M Crawford K Bogart S Lee R Kaplar W ChowGrowth and characterization of blue and near-ultraviolet light-emitting diodes onbulk GaN [5530-6]X Cao S LeBoeuf S Arthur D Merfeld M DEvelynMg-doped AI-rich AIGaN alloys for deep UV emitters [5530-7]M Nakarmi K Kim K Zhu J Lin H JiangPerformance and application of high-power ultraviolet AlGaInN light-emittingdiodes [5530-8]1 Han S Jeon M Gherasimova 1 Su G Cui H Peng E Makarona Y He Y SongA Nurmikko L ZhouW Goetz M KramesCHARiCnRIZA1IONLED photometric calibrations at the National Institute of Standards andTechnology and future measurementneeds of LEDs [5530-10]C Miller Y Zong Y 0000LED white light visual equivalence [5530-11]C YouColor rendering and luminous efficacy of white LED spectra [5530-12]Y 0000Rapid photo-goniometric technique for LED emission characterization [5530-13]P Boher M Luet T LerouxPosition-dependent analysis of light extraction of GaN-based LEDs [5530-14]C Sun T Lee C LinWhite LED performance [5530-15]Y Gu N Narendran J FreyssinierSSTElS IA massive primary approach to solid state lighting [5530-18]

S PaoliniLED illumination control and color mixing with Engineered Diffusers [5530-19]T Sales S Chakmakjian D Schertler G MorrisApplication of high-brightness LEDs in aircraft position lights [5530-20]N Machi S Mangum 1 SingerA spectrally tunable solid-state source for radiometric photometric andcolorimetric applications [5530-21]I Frye S Brown G Eppeldauer Y Ohno

~Investigation of the spectral properties of LED-based lIR16s for generalillumination [5530-53]D Brown D Nicol A Payne I FergusonHigh-power LEDs for plant cultivation [5530-24]G Tamulaitis P Duchovskis Z Bliznikas K Breive R Ulinskaite A Brazaityte ANovickovas A ZukauskasM ShurApplications of deep UV LEDs to chemical and biological sensing [5530-25]P Dasgupta Q Li H Temkin M Crawford A Fischer A Allerman K Bogart S LeeShort-range communication with ultraviolet LEDs [5530-49]A Siegel G Shaw J Model

ESSINGPA(KAGIEmerging low-cost LED thermal management materials [5530-27]C ZwebenBevelled-sidewalls formation and its effect on the light output of GaInN MQW LEDchips [5530-28]1 Hsu C Huang W Yeh 1 Tsay Y Guo C Chuo C Lin C Sun S PanChip-scale thermal management of high-brightness LED packages [5530-29]M Arik S Weaver

Deep-ultraviolet LEDs fabricated in AlInGaN using MEMOCVD [5530-30]M KhanUniform white light distribution with low loss from colored LEDs using polymer-doped polymer mixingrods [5530-32]C Deller G Smith 1 FranklinIII-nitride blue and UV photonic-crystallight-emitting diodes [5530-33]1 Shakya K Kim T Oder 1 Lin H JiangStudy of short-term instabilities of InGaNGaN light-emitting diodes by means ofcapacitance-voltagemeasurements and deep-level transient spectroscopy [5530-36]G Meneghesso M Meneghini S Levada E Zanoni A Cavallini A Castaldini VHarle T Zahner U Zehnder

High CRI phosphor blends for near-UV LED lamps [5530-37]E Radkov A Setlur Z Brown 1 ReginelliPerformance of phosphor-coated LED optics in ray trace simulations [5530-40]

A Borbely S JohnsonConcentration and crystallite size dependence of the photoluminescence in YAGCenanophosphor 3+

[5530-39]R Ovalle A Arredondo L Diaz-Torres P Salas C Angeles R Rodriguez MMeneses E De la RosaHE EBLSuccessful design of PV power systems for solid-state lighting applications [5530-41]1 Thornton B StaffordPerformance of PV-powered LED lighting systems for buildings [5530-42]y Zhou N NarendranGroup III-nitride alloys as photovoltaic materials [5530-43]1 Ager III 1 Wu K Yu R Jones S Li W Walukiewicz E Haller H Lu W SchaffGrowing pains for new energy-saving technologies [5530-44]S KurtzEffects of ordering on the optical properties of GalnP [5530-45] 2

D Levi 1 Geisz B Johs

Electrode design for InGaNsapphire LEDs based on multiple thin ohmic-metalpatches [5530-46]S LeeColor perception under illumination by quadrichromatic solid-state lamp [5530-47]R Stanikunas H Vaitkevicius A Svegzda V Viliunas Z Bliznikas K Breive RVaicekauskas A NovickovasG Kurilcik A Zukauskas R Gaska M ShurWhite organic light-emitting diodes with high efficiency and stable color coordinates[5530-48]C Lee N Lee 1 Song D Hwang

Conference CommitteeSymposium ChairDavid L Begley Ball Aerospace amp Technologies Corporation (USA)Program ChairIan T Ferguson Georgia Institute of Technology (USA)Conference ChairsIan T Ferguson Georgia Institute of Technology (USA)Nadarajah Narendran Rensselaer Polytechnic Institute (USA)Steven P DenBaars University of CaliforniaSanta Barbara (USA)John C Carrano DARPA (USA)Program CommitteeSrinath K Aanegola GELcore LLC (USA)William J Cassarly Optical Research Associates (USA)Lianghui Chen Institute of Semiconductors (China)Makarand H Chipalkatti OSRAM Opto Semiconductors GmbH (USA)Kevin J Dowling Color Kinetics Inc (USA)

Ivan Eliashevich Gelcore LLC (USA)Volker Harle OSRAM Opto Semiconductors GmbH (Germany)Stephen G Johnson Lawrence Berkeley National Laboratory (USA)Bernd Keller Cree Lighting (USA)Kevin F Leadford Lithonia Lighting (USA)Yung-Sheng Liu Industrial Technology Research Institute (Taiwan)Paul S Martin Lumileds Lighting LLC (USA)Shuji Nakamura University of CaliforniaSanta Barbara (USA)Seong-Ju Park Kwangju Institute of Science and Technology (SouthKorea)Yoon-Soo Park Seoul National University (South Korea)E Fred Schubert Rensselaer Polytechnic Institute (USA)Jerry A Simmons Sandia National Laboratory (USA)Cheolsoo Sone Samsung Advanced Institute of Technology (South Korea)Robert V Steele Strategies Unlimited (USA)Tsunemasa Taguchi Yamaguchi University (Japan)Brent K Wagner Georgia Institute of Technology (USA)Session ChairsI OverviewIan T Ferguson Georgia Institute of Technology (USA)vii

2 LED ApplicationsJuan Carlos Mifiano Universidad Politecnica de Madrid (Spain)3 Organic Solid State LightingGhassan E Jabbour Arizona State University (USA)4 Sources IJohn C Carrano DARPA (USA)5 CharacterizationSteven P DenBaars University of CaliforniaSanta Barbara (USA)6 Systems IKevin F Leadford Lithonia Lighting (USA)7 Systems IIIan T Ferguson Georgia Institute of Technology (USA)8 ProcessingPackagingEdward D Petrow Lincoln Technical Services (USA)9 Sources IIChris L Bohler GELcore LLC (USA)10 PhosphorsChristopher J Summers Georgia Institute of Technology (USA)11 RenewableChristiana Honsberg Georgia Institute of Technology (USA)V III

IntroductionThis Fourth International Conference on Solid State Lighting took place during theSPIE Annual Meeting in Denver Colorado on August 3-6 2004

Contained in these proceedings are submitted papers of 40 invited andcontributing attendees of this meeting The topics covered by these papersrange from light measurement and characterization standards to LED processingtechniques to the possible applications of solid state light sources It is evidentfrom the quantity and quality of these proceedings that solid state lighting as atechnology and an industry is a rapidly developing area of science andtechnologyThe conference chairs would like to thank SPIE for hosting this meeting as well asthe program committee members authors and session chairs for making thismeeting a technical success that provides valued and timely research on SolidState LightingIan T FergusonNadarajah NarendranSteven P DenBaarsJohn C CarranoIX

The sources that are mixed are two sets of 5 mm RGB LEOs denoted as Alpha group and Beta group Each groupconsists of a triad of 3 LEOS It is desirable for the individual angular source distributions within a set to be as similar aspossible The LEOs were selected from a larger pool of 5 mm LEOs all of which had been measured using aphotogoniometer described elsewhere A cross-section of the angular intensity distribution of the Alpha and Beta groupLEOs as measured by the photogoniorneter is shown in Figure I Spectra of the LEOs were obtained via an OceanOptics S02000 tiber optic spectrometer coupled to an Oriel 70491 integrating sphere and associated software 1931 CIEcoordinates for the LEOs were derived from the respective spectral power distributions These source CIE coordinatesand the LED peak spectral wavelengths are given in Table 1

b) Beta Group1------ -- ---

I

a) Alpha Group

-- Redi-Green Blue

40

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bull tobullbullbullbull

-- Red

- Gr e e n Blue I

--40 -20J 20

Angle from Normal 1deg)

--40 -21) 0 LIJ

Angle from Normal deg140

Figure 1 Measured angular distribution of the source LEOs a) Alpha group b) Beta group

Alpha Group CIE x CIEy Beta Group CIE x CIE y

Alpha Red (642nm) 0701 0294 Beta Red (632nm) 0691 0301

Alpha Green (509nm) 0114 0681 Beta Green (513nm) 0162 0674

Alpha Blue (462nm) 0135 0058 Beta Blue (460nm) 0138 0062

Table 1 1931 CIE coordinates and peak wavelength of the source LEOs as measured using a spectrometer

The Alpha group LEOs are better matched in angle than the Beta group but the Beta group is superior in terms of colourfor RGB mixing as the spectra of the Beta peaks are more widely spread (The spectral peaks of Alpha green and blueare closer together (Table I )) For the computer modeling a separate source model was generated for each LED based onthese measured profiles

The experimental setup for measurements is shown in Figure 2a The Alpha or Beta RGB LED triad was mounted asclose as possible to the end of the mixing rod The centre point of the LED array was aligned with the rods axis Afrosted glass screen (dimensions 120 mm x 955 mm) was positioned 4 ern or 15 ern from the exit end of the rodPhotographs of the transmitted output distributions were taken with an Olympus C-4000 ZOOM digital cameraTransmittance measurements were performed using the Alpha LED source array and the clear and clear + TRIMMdiffuser rods with the output end coupled to the entrance port of an Oriel 70491 integrating sphere A BPW21photodiode was attached to the detector port of the integrating sphere and readings taken with a Data Precision OP 100Multimeter The ratio of the transmitted to incident readings were taken using measurements of the bare LED array asthe total incident light


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20 40 60 80 100 120

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a) b)

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Colour erE x20 40 60 30 100 1~0

Colour CIE I20 40 60 80 100 120

20 ~O 60 80 100lIIlll

iiI

120

41 I~ 05

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a) b)-- W

o

~ ~-

c) d)

Colour CIE x

20 40 60 80 100 120Colour CIE Y

20 40 60 80 100 120

bullbull o 55 o j


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(mm)




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a) b)

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Colour erE x20 40 60 30 100 1~0

Colour CIE I20 40 60 80 100 120

20 ~O 60 80 100lIIlll

iiI

120

41 I~ 05

lmiddot



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a) b)-- W

o

~ ~-

c) d)

Colour CIE x

20 40 60 80 100 120Colour CIE Y

20 40 60 80 100 120

bullbull o 55 o j


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bullbullbullbull

05



11III







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(mm)




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4 RESULTS




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Colour erE x20 40 60 30 100 1~0

Colour CIE I20 40 60 80 100 120

20 ~O 60 80 100lIIlll

iiI

120

41 I~ 05

lmiddot



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~ ~-

c) d)

Colour CIE x

20 40 60 80 100 120Colour CIE Y

20 40 60 80 100 120

bullbull o 55 o j


~ vl Io Ibullfi 20 40 60 80 100 120

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05



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(mm)




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ISSN 0277-786XISBN Q-8194-5446-X
























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Colour erE x20 40 60 30 100 1~0

Colour CIE I20 40 60 80 100 120

20 ~O 60 80 100lIIlll

iiI

120

41 I~ 05

lmiddot



IIIIIl


a) b)-- W

o

~ ~-

c) d)

Colour CIE x

20 40 60 80 100 120Colour CIE Y

20 40 60 80 100 120

bullbull o 55 o j


~ vl Io Ibullfi 20 40 60 80 100 120

bullbullbullbull

05



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(mm)




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ISSN 0277-786XISBN Q-8194-5446-X



























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