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Kleuraspecten van
             LED toestellen

Richard Vanraes
Peter Hanselaer
Laboratorium voor Lichttechnologie, Gent
KAHO Sint-Lieven
KU Leuven
Outline



•   Light&Lighting Laboratory
•   Colorimetry in a nutshell
•   Colorimetry of LEDs
•   RGB or phosphor white?
•   Impact of junction temperature?
•   Impact of viewing angle?
•   Impact of operating time?
•   What about colour rendering ?


                               2
Light&Lighting Laboratory:
                 the team




        3
Light&Lighting Laboratory:
                                           topics

 Lighting             Optical design


            Measurement
              Facilities


Appearance             New Light
                        Sources  4
Light&Lighting Laboratory:
                                                      activities

PhD research items                 Industrial consultancy

• LEDs and general lighting        • 3 consortia
• OLED                             • >70 companies
• remote phosphor LEDs             • Bilateral projects
• lighting in the operating room   • Projects with non-profit
• colour rendering                        organisations
• gloss perception                 • Measurements
• colour appearance                • Courses
• ray tracing                      • Lectures
• scattering and fluorescence
• spectral response solar cells
                                             5
Combination of research and consultancy

      PhD Research



                                    Education
                                     Society



    Industrial Consultancy
Light&Lighting Laboratory:
                                   measurement facilities

Spectrometers/ CCD detectors




                                         7
Light&Lighting Laboratory:
            measurement facilities




Near field goniometers
                   8
Colorimetry in a nutshell:
                colour classification


Munsell
Hue 5Y                 5Y 8/12




                   9
Colorimetry in a nutshell:
                                 colour matching

                    Three primary sources




Test colour K       K  AA  BB  CC
with luminance LK   LK  A.LA  B.LB  C.LC

                                10
Colorimetry in a nutshell:
                                            trichromatic values




 Primaries

Trichromatic values   x 0.706       x 0.863        x 0.863
Kleurcomponenten
       X,Y,Z



                                            
                                              11
Colorimetry in a nutshell:
                                 colour coordinates




Ignoring brightness, only two numbers are
    needed: colour coordinates (x,y)
            (Kleurcoördinaten)

                X
          x
             X Y  Z
                Y
          y
             X Y  Z
                                  12
Characteristics   Colorimetry in a nutshell:
                      chromaticity diagram


                       • Spectrum locus
                       • Additive mixing
                       • Purity, saturation
                       • Colour gamut
                       • Primary colours




                          13
Colorimetry in a nutshell:
                         correlated colour temperature




The correlated colour temperature is the
temperature of a Planckian radiator having
the chromaticity nearest the chromaticity
associated with the given spectral distribution
on a diagram where the (CIE1931 standard
observer based) u, v coordinates of the
Planckian locus and the test stimulus are
depicted.


                                      14
Colorimetry in a nutshell:
correlated colour temperature


  Black Body Locus




  EN 12464
  • CCT<3300 K :
   “warm white”
  • 3300 K< CCT< 5300 K:
   “neutral white”
  • CCT>5300K:
   “cool daylight”



             15
Colorimetry in a nutshell:
                                 colour rendering




The colour rendering index CRI of a light
   source is a measure of the shift in
  chromaticity of a set of objects when
    they are lighted by the source as
 compared to be lighted by a reference
      source of comparable colour
               temperature.


                                 16
Colorimetry in a nutshell:
                                           colour rendering

Testsamples (8 of 14)   Testlamp

                                         Colour coordinates



                                         <colour differences>
                        Standardlamp



                                         Colour coordinates



                                           17
Colorimetry in a nutshell:
                                   chromatic adaptation


• The visual system is able to partially or
  completely disaccount for the colour of the
  illuminant such that the white of the illuminant
  is always perceived as “white” (complete
  adaptation)
• This is accomplished by changing the
  sensitivities of the red, green and blue visual
  channel.


                                       18
Colorimetry in a nutshell:
        chromatic adaptation




*




            19
Colorimetry in a nutshell:
             colour matching




*                *




            20
Colorimetry of LEDs:
                                                                                     spectrum

E




                               Spectrale stralingsintensiteit
                                                                1500


                                    1240                        1200                                          LED1

                           (nm) 




                                       (mW/sr.nm)
 Band gap Eg                                                     900

                                   Eg (eV )                      600

                                                                 300

                                                                   0
                                                                   350   400   450    500   550   600   650     700   750
                                                                                      Golflengte (nm)




1. Peak wavelength is determined by bandgap Eg
                                     c
                                    1240
         E  Eg (eV )  h.f  h. 
                                   (nm)
2. Number of photons: drive current and recombination
          probability
                                                                                     21
Colorimetry of LEDs:
              chromaticity




High purity colours
Wide colour gamut
possible
No direct generation
of white light

CIE chromaticity
         22
Colorimetry of LEDs:
RGB additive mixing




   23
Colorimetry of LEDs:
Phosphor White LEDs




    24
Colorimetry of LEDs:
Phosphor White LEDs




    25
RGB or Phosphor White?
                                            Experiment



LEDs from 3 manufacturers
• 1 phosphor-white package (350 mA)
• 1 red-green-blue package

Comparison of consumed power for same
• luminous flux
• colour coordinates
• heat sink
with PW as reference


                                        26
RGB or Phosphor White?
                                                                               Results

                                                 P (W)     eff. (lm/W)    P (W)   eff. (lm/W)
MFR           flux (lm)           CIE (x,y)
                                                  PW            PW         RGB        RGB
M1              84.1             (0.31, 0.33)     1.16        72.5        2.44       34.5
M2              45.9             (0.32, 0.33)     1.06        43.3        2.50       18.4
M3              77.6             (0.30, 0.32)     1.11        69.9        2.61       29.7

        1,8
        1,6
        1,4
                                                                                         PW
        1,2
                                                                                         R
P (W)




          1
        0,8                                                                              G
        0,6
                                                                                         B
        0,4
        0,2
          0
                          M1
                          Cree                    M2
                                                Lumileds                 M3
                                                                         SSC
                                                                           27
Impact of junction temperature?
                                               Spectrum


                             E

                                                             1240
                              Band gap Eg         (nm) 
                                                            Eg (eV )




Decrease of the bandgap: increase of wavelength
Decrease of recombination rate: decrease of flux

                                            28
Impact of junction temperature?
                                                                     Chromaticity

          piek      I        U        x         y
         (nm/°C)   (cd/°C)    (V/°C)    (1/°C)     (1/°C)

 Red      0.19     - 0.058   - 0.0012   90 E-6    - 90 E-6

Green     0.11     - 0.016   - 0.0040   42 E-5    - 23 E-5

Yellow    0.14     - 0.052   - 0.0019   55 E-5    - 55 E-5




                                                               29
Impact of junction temperature?
                   Active cooling




               30
Impact of junction temperature?
                                   LuxeonIII U(junction T) for series 1 (used) Forward voltage
        2.45


        2.40


        2.35


        2.30


        2.25

                                                                                                         1: 10 µA
        2.20
                                                           y = -0.0026x + 2.4443                         1: 100 µA
U (V)




                                                                 R2 = 0.999                              2: 10 µA
        2.15
                                                                                                         2: 100 µA

        2.10


        2.05


        2.00


        1.95


        1.90
               20   30   40   50        60            70           80              90   100        110
                                             temperature (°C)




                                                    nk             
                                        U f T    ln  I m   a  T  b
                                                   e               
                                                                                              31
Impact of junction temperature?
                  Determination




              32
Impact of junction temperature
                                               Self heating




                          With and without heat sink
                          Different ambient temperature




Luminous flux is dependent on
heat sink, position of heat sink, . . .
                                          33
Impact of viewing angle?
                           Chromaticity




                                I (85°)



        flux
I(0°)



                       34
Impact of viewing angle?
                                              Spectrum




Negligible impact when using
remote phosphor LEDs



                                       35
Impact of operating time?
                          Chromaticity




                           Degradation of
Experiments                 the phosphor




                      36
Impact of operating time?
                                                                                          CCT and CRI

                                                                                         CRI                        Verschil in %
                   CCT [K]                  Verschil in %
                                                                              September Januari        April   Januari tov April tov
          September Januari   April   Januari tov    April tov
                                                                                 2010    2011          2011    september september
            2010     2011     2011    september     september
                                                                 Lamp 1          90        89           89        -1%        -1%
Lamp 1      4186      4066    4075       -3%            -3%
            6876      6637    6818       -3%            -1%      Lamp 2          72        73           73        1%         1%
Lamp 2
Lamp 3      3709      3653    3701       -2%            0%       Lamp 3          76        78           80        3%         5%
            4016      3874    3834       -4%            -5%      Lamp 4          69        70           69        1%         0%
Lamp 4
Lamp 5      4207      4077    4128       -3%            -2%      Lamp 5          76        78           79        3%         4%
Lamp 6      3194      3167    3194       -1%            0%       Lamp 6          65        66           65        1%         1%
Lamp 7      3307      3153    3175       -5%            -4%      Lamp 7          71        71           71        0%         0%
Lamp 8      3853      3717    3743       -4%            -3%      Lamp 8          77        77           77        0%         0%
Lamp 9      3365      3307    3326       -2%            -1%      Lamp 9          88        88           88        0%         0%
Lamp 10     3678      3470    3670       -6%            0%       Lamp 10         78        77           80        -1%        3%
Lamp 11     4733      4586    4625       -3%            -2%      Lamp 11         65        65           65        0%         0%
Lamp 12     5329      5037    5104       -5%            -4%      Lamp 12         73        72           73        -1%        0%


                                                                 gemiddelde      75        76           76        0%         1%
                                                                 mediaan         76        77           77        1%         1%

                    IEC PAS 62717:
                    CRI after 6000 h: maximum -5
                    CCT after 6000 h: within 1 class (100 K)
                                                                                                  37
What about colour rendering?
                                                            Problem


Reference Illuminant                             Ra=83
                                                 Ra=70
                                                 Ra=60
                                                 Ra=100
                                                 Ra=85
                                                 Ra=50




Large colour differences towards reference
                           
                   low quality !
                      Kevin.Smet@kahosl.be
                                                    38
                                                                   38
What about colour rendering?
                                         Memory colours




The more similar a light source renders the familiar
  object colours to their memory colours,
      the better the colour quality.
                                         39
What about colour rendering?
                              Determination of Memory colours

    Colour appearance rating of real familiar objects




The closer the test illuminant reaches the memory
colour of 10 objects, the higher the MCRI
                                             40
                   Kevin.Smet@kahosl.be                     40
What about colour rendering?
                                             Experimental validation

• Aspects of colour quality investigated

  – Preference/attractiveness (appreciation)
  – Naturalness

• Thirteen colour quality metrics (CIE TC 1-69)

• Combining results of 9 psychophysical studies


     Correlation between 13 metric predictions and

     all the visual data is calculated.

                                                    41
                      Kevin.Smet@kahosl.be                         41
What about colour rendering?
                                            Experimental validation




Memory metric for preference/attractiveness: ravg = 0.88

GAI_Ra for naturalness: ravg = 0.85

                                                   42
                     Kevin.Smet@kahosl.be                         42
What about colour rendering?
                                                Optimizing LED clusters



Xb  Xg  Xr  Xw  X
 Yb  Yg  Yr  Yw  Y
 Zb  Zg  Zr  Zw  Z

         xi
     Xi    .Yi
         yi
         zi
     Zi  .Yi
         yi


Optimum MCRI
ánd efficacy



                                                       43
                         Kevin.Smet@kahosl.be                         43
What about colour rendering?
                                                                      Visual performance

   Visual experiment with 2700K setting:


MEAN/MEDIAN         Attractiveness   Preference         Naturalness   Vividness   Memory

Sa optimized LED      7.8 / 8.0       7.9 / 8.0           7.2 /8.0    7.4 /8.0    7.9 /8.0

 RGB LED cluster      6.0 / 6.0       5.6 / 6.0           4.2 / 4.5   6.3 / 7.0   4.8 / 5.0

Incandescent lamp     5.8 / 6.0       6.0 / 6.0           6.9 / 7.0   6.2 / 6.5   6.5 / 6.0


• Sa optimized LED lamp scored significantly better (p<0.05)
  than the incandescent source for attractiveness, preference and
  memory.

• No significant differences for naturalness and vividness !


                                                                          44
                                           Kevin.Smet@kahosl.be                               44
www.lichttechnologie.be:
         daar brandt de lamp . . .

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Kleuraspecten van LED toestellen - KAHO / Laboratorium voor Lichttechnologie

  • 1. Kleuraspecten van LED toestellen Richard Vanraes Peter Hanselaer Laboratorium voor Lichttechnologie, Gent KAHO Sint-Lieven KU Leuven
  • 2. Outline • Light&Lighting Laboratory • Colorimetry in a nutshell • Colorimetry of LEDs • RGB or phosphor white? • Impact of junction temperature? • Impact of viewing angle? • Impact of operating time? • What about colour rendering ? 2
  • 4. Light&Lighting Laboratory: topics Lighting Optical design Measurement Facilities Appearance New Light Sources 4
  • 5. Light&Lighting Laboratory: activities PhD research items Industrial consultancy • LEDs and general lighting • 3 consortia • OLED • >70 companies • remote phosphor LEDs • Bilateral projects • lighting in the operating room • Projects with non-profit • colour rendering organisations • gloss perception • Measurements • colour appearance • Courses • ray tracing • Lectures • scattering and fluorescence • spectral response solar cells 5
  • 6. Combination of research and consultancy PhD Research Education Society Industrial Consultancy
  • 7. Light&Lighting Laboratory: measurement facilities Spectrometers/ CCD detectors 7
  • 8. Light&Lighting Laboratory: measurement facilities Near field goniometers 8
  • 9. Colorimetry in a nutshell: colour classification Munsell Hue 5Y 5Y 8/12 9
  • 10. Colorimetry in a nutshell: colour matching Three primary sources Test colour K K  AA  BB  CC with luminance LK LK  A.LA  B.LB  C.LC 10
  • 11. Colorimetry in a nutshell: trichromatic values Primaries Trichromatic values x 0.706 x 0.863 x 0.863 Kleurcomponenten X,Y,Z    11
  • 12. Colorimetry in a nutshell: colour coordinates Ignoring brightness, only two numbers are needed: colour coordinates (x,y) (Kleurcoördinaten) X x X Y  Z Y y X Y  Z 12
  • 13. Characteristics Colorimetry in a nutshell: chromaticity diagram • Spectrum locus • Additive mixing • Purity, saturation • Colour gamut • Primary colours 13
  • 14. Colorimetry in a nutshell: correlated colour temperature The correlated colour temperature is the temperature of a Planckian radiator having the chromaticity nearest the chromaticity associated with the given spectral distribution on a diagram where the (CIE1931 standard observer based) u, v coordinates of the Planckian locus and the test stimulus are depicted. 14
  • 15. Colorimetry in a nutshell: correlated colour temperature Black Body Locus EN 12464 • CCT<3300 K : “warm white” • 3300 K< CCT< 5300 K: “neutral white” • CCT>5300K: “cool daylight” 15
  • 16. Colorimetry in a nutshell: colour rendering The colour rendering index CRI of a light source is a measure of the shift in chromaticity of a set of objects when they are lighted by the source as compared to be lighted by a reference source of comparable colour temperature. 16
  • 17. Colorimetry in a nutshell: colour rendering Testsamples (8 of 14) Testlamp Colour coordinates <colour differences> Standardlamp Colour coordinates 17
  • 18. Colorimetry in a nutshell: chromatic adaptation • The visual system is able to partially or completely disaccount for the colour of the illuminant such that the white of the illuminant is always perceived as “white” (complete adaptation) • This is accomplished by changing the sensitivities of the red, green and blue visual channel. 18
  • 19. Colorimetry in a nutshell: chromatic adaptation * 19
  • 20. Colorimetry in a nutshell: colour matching * * 20
  • 21. Colorimetry of LEDs: spectrum E Spectrale stralingsintensiteit 1500 1240 1200 LED1  (nm)  (mW/sr.nm) Band gap Eg 900 Eg (eV ) 600 300 0 350 400 450 500 550 600 650 700 750 Golflengte (nm) 1. Peak wavelength is determined by bandgap Eg c 1240 E  Eg (eV )  h.f  h.    (nm) 2. Number of photons: drive current and recombination probability 21
  • 22. Colorimetry of LEDs: chromaticity High purity colours Wide colour gamut possible No direct generation of white light CIE chromaticity 22
  • 23. Colorimetry of LEDs: RGB additive mixing 23
  • 26. RGB or Phosphor White? Experiment LEDs from 3 manufacturers • 1 phosphor-white package (350 mA) • 1 red-green-blue package Comparison of consumed power for same • luminous flux • colour coordinates • heat sink with PW as reference 26
  • 27. RGB or Phosphor White? Results P (W) eff. (lm/W) P (W) eff. (lm/W) MFR flux (lm) CIE (x,y) PW PW RGB RGB M1 84.1 (0.31, 0.33) 1.16 72.5 2.44 34.5 M2 45.9 (0.32, 0.33) 1.06 43.3 2.50 18.4 M3 77.6 (0.30, 0.32) 1.11 69.9 2.61 29.7 1,8 1,6 1,4 PW 1,2 R P (W) 1 0,8 G 0,6 B 0,4 0,2 0 M1 Cree M2 Lumileds M3 SSC 27
  • 28. Impact of junction temperature? Spectrum E 1240 Band gap Eg  (nm)  Eg (eV ) Decrease of the bandgap: increase of wavelength Decrease of recombination rate: decrease of flux 28
  • 29. Impact of junction temperature? Chromaticity piek I U x y (nm/°C) (cd/°C) (V/°C) (1/°C) (1/°C) Red 0.19 - 0.058 - 0.0012 90 E-6 - 90 E-6 Green 0.11 - 0.016 - 0.0040 42 E-5 - 23 E-5 Yellow 0.14 - 0.052 - 0.0019 55 E-5 - 55 E-5 29
  • 30. Impact of junction temperature? Active cooling 30
  • 31. Impact of junction temperature? LuxeonIII U(junction T) for series 1 (used) Forward voltage 2.45 2.40 2.35 2.30 2.25 1: 10 µA 2.20 y = -0.0026x + 2.4443 1: 100 µA U (V) R2 = 0.999 2: 10 µA 2.15 2: 100 µA 2.10 2.05 2.00 1.95 1.90 20 30 40 50 60 70 80 90 100 110 temperature (°C)  nk  U f T    ln  I m   a  T  b e  31
  • 32. Impact of junction temperature? Determination 32
  • 33. Impact of junction temperature Self heating With and without heat sink Different ambient temperature Luminous flux is dependent on heat sink, position of heat sink, . . . 33
  • 34. Impact of viewing angle? Chromaticity I (85°) flux I(0°) 34
  • 35. Impact of viewing angle? Spectrum Negligible impact when using remote phosphor LEDs 35
  • 36. Impact of operating time? Chromaticity Degradation of Experiments the phosphor 36
  • 37. Impact of operating time? CCT and CRI CRI Verschil in % CCT [K] Verschil in % September Januari April Januari tov April tov September Januari April Januari tov April tov 2010 2011 2011 september september 2010 2011 2011 september september Lamp 1 90 89 89 -1% -1% Lamp 1 4186 4066 4075 -3% -3% 6876 6637 6818 -3% -1% Lamp 2 72 73 73 1% 1% Lamp 2 Lamp 3 3709 3653 3701 -2% 0% Lamp 3 76 78 80 3% 5% 4016 3874 3834 -4% -5% Lamp 4 69 70 69 1% 0% Lamp 4 Lamp 5 4207 4077 4128 -3% -2% Lamp 5 76 78 79 3% 4% Lamp 6 3194 3167 3194 -1% 0% Lamp 6 65 66 65 1% 1% Lamp 7 3307 3153 3175 -5% -4% Lamp 7 71 71 71 0% 0% Lamp 8 3853 3717 3743 -4% -3% Lamp 8 77 77 77 0% 0% Lamp 9 3365 3307 3326 -2% -1% Lamp 9 88 88 88 0% 0% Lamp 10 3678 3470 3670 -6% 0% Lamp 10 78 77 80 -1% 3% Lamp 11 4733 4586 4625 -3% -2% Lamp 11 65 65 65 0% 0% Lamp 12 5329 5037 5104 -5% -4% Lamp 12 73 72 73 -1% 0% gemiddelde 75 76 76 0% 1% mediaan 76 77 77 1% 1% IEC PAS 62717: CRI after 6000 h: maximum -5 CCT after 6000 h: within 1 class (100 K) 37
  • 38. What about colour rendering? Problem Reference Illuminant Ra=83 Ra=70 Ra=60 Ra=100 Ra=85 Ra=50 Large colour differences towards reference  low quality ! Kevin.Smet@kahosl.be 38 38
  • 39. What about colour rendering? Memory colours The more similar a light source renders the familiar object colours to their memory colours, the better the colour quality. 39
  • 40. What about colour rendering? Determination of Memory colours Colour appearance rating of real familiar objects The closer the test illuminant reaches the memory colour of 10 objects, the higher the MCRI 40 Kevin.Smet@kahosl.be 40
  • 41. What about colour rendering? Experimental validation • Aspects of colour quality investigated – Preference/attractiveness (appreciation) – Naturalness • Thirteen colour quality metrics (CIE TC 1-69) • Combining results of 9 psychophysical studies Correlation between 13 metric predictions and all the visual data is calculated. 41 Kevin.Smet@kahosl.be 41
  • 42. What about colour rendering? Experimental validation Memory metric for preference/attractiveness: ravg = 0.88 GAI_Ra for naturalness: ravg = 0.85 42 Kevin.Smet@kahosl.be 42
  • 43. What about colour rendering? Optimizing LED clusters Xb  Xg  Xr  Xw  X Yb  Yg  Yr  Yw  Y Zb  Zg  Zr  Zw  Z xi Xi  .Yi yi zi Zi  .Yi yi Optimum MCRI ánd efficacy 43 Kevin.Smet@kahosl.be 43
  • 44. What about colour rendering? Visual performance Visual experiment with 2700K setting: MEAN/MEDIAN Attractiveness Preference Naturalness Vividness Memory Sa optimized LED 7.8 / 8.0 7.9 / 8.0 7.2 /8.0 7.4 /8.0 7.9 /8.0 RGB LED cluster 6.0 / 6.0 5.6 / 6.0 4.2 / 4.5 6.3 / 7.0 4.8 / 5.0 Incandescent lamp 5.8 / 6.0 6.0 / 6.0 6.9 / 7.0 6.2 / 6.5 6.5 / 6.0 • Sa optimized LED lamp scored significantly better (p<0.05) than the incandescent source for attractiveness, preference and memory. • No significant differences for naturalness and vividness ! 44 Kevin.Smet@kahosl.be 44
  • 45. www.lichttechnologie.be: daar brandt de lamp . . .