Download - Color Consistency
Color Consistency
Willem Sillevis Smitt, XicatoLight and Building, March 2016
"The color of the object illuminated partakes of the color of that which illuminates it"
- Leonardo Da Vinci
Lighting Aspects of Object Rendition
Saturated Colors• Color Rendering• TM30, IES CIE
Whites or light colors• White point consistency• MacAdam ellipses, SDCM (Standard Deviation of Color
Matching)
For Lightly Colored Surfaces Color Consistency of the Light Sources is Critical
On a white wall, light is just like paint
PART 1: Framework for Describing White Light Consistency
Quantifying White Points and Color
Do you know which colors these are?
(0.4599, 0.4106)(0.4369, 0.4041)(0.4053, 0.3907)(0.3804, 0.3767)
Quantifying White Points and Color
Do you know which color these are?
(0.4599, 0.4106)(0.4369, 0.4041)(0.4053, 0.3907)(0.3804, 0.3767)
CIE 1931, “x,y” coordinates
Or these?
(0.2625, 0.5274)(0.2505, 0.5214)(0.2357, 0.5113)(0.2251, 0.5015)
Quantifying White Points and Color
Do you know which color these are?
(0.4599, 0.4106)(0.4369, 0.4041)(0.4053, 0.3907)(0.3804, 0.3767)
CIE 1931, “x,y” coordinates
Or these?
(0.2625, 0.5274)(0.2505, 0.5214)(0.2357, 0.5113)(0.2251, 0.5015)
CIE 1976, “u’, v’” coordinates
Quantifying White Points and Color
Do you know which color these are?
(0.4599, 0.4106)(0.4369, 0.4041)(0.4053, 0.3907)(0.3804, 0.3767)
CIE 1931, “x,y” coordinates
Or these?
(0.2625, 0.5274)(0.2505, 0.5214)(0.2357, 0.5113)(0.2251, 0.5015)
CIE 1976, “u’, v’” coordinates
How about these?
2,700K Duv 0.0003,000K Duv 0.0003,500K Duv 0.0004,000K Duv 0.000
CCT and CIE 1960 DuvMore intuitive metric for white
Quantifying White Points and Color
CIE 1931, “x,y” coordinates CIE 1976, “u’, v’” coordinates
0K 2,500K 5,000K 7,500K 10,000K 12,500K
-0.006
-0.003
0.000
0.003
0.006
Correlated Color Temperature
Duv
Simple metric specific for white
Quantifying White Points and Color
0K 2,500K 5,000K 7,500K 10,000K 12,500K
-0.006
-0.003
0.000
0.003
0.006
Correlated Color Temperature
Duv
Duv positive: Greenish / Yellowish
Duv negative: Pinkish
Quantifying Color Differences
• MacAdam ellipses• u’v’ CIE 1976 space
More up to date:• SDCM (Standard Deviation of
Color Matching)
McAdam Ellipses Around 3,000K
2800K 2900K 3000K 3100K 3200K
-0.006
-0.004
-0.002
0
0.002
0.004
0.006
2McAdam3McAdam5McAdam
CCT
Duv
0.24 0.245 0.25 0.255 0.260.51
0.515
0.52
0.525
0.53
2McAdam3McAdam5McAdam
V’
U’
CIE 1976, “u’, v’” coordinates CCT and CIE 1960 Duv
Acceptable and Unacceptable Color Differences
2800K 2900K 3000K 3100K 3200K
-0.006
-0.004
-0.002
0
0.002
0.004
0.006
1x2McAdam2McAdam3McAdam5McAdam
CCT
duv
Red Zone:>4 McAdamNot fit for most lighting applications
Yellow Zone:2-4 McAdamNon-critical lighting applications
Green zone:1x2McAdamFor accent and architectural lightingThis corresponds with +/- 0.001Duv and +/- 50K
Energy Star du’v’ 0.006
Conclusions of Part 1:
• CCT – Duv is a more intuitive framework for describing whites and differences in white than
CIE 1931 (x,y) or CIE 1976 (u’,v’)
• 1x2McAdam ellipses is a necessary requirement for non-observable white differences in
accent and architectural lighting
• 1x2McAdam ellipse corresponds with +/- 0.001 Duv and +/- 50K (around 3,000K)
Recommended specification for color consistency:
1x2 McAdam ellipse
Or
+/- 50K CCT AND +/- 0.001Duv
PART 2: Important Steps to Achieve Color Consistency
Step 1: Product Design and Process Control
• Accurate matching of primaries• Keep if consistent over the life of the product
Color Consistency Over the Life of the Product
• Results from external LM-80 testing on Xicato Modules
– At maximum rated current and temperature– 10,000 hours
• Plot shows individual parts at 0h and 10,000h – (0 and 10,000h connected by a line)
• Worst case shift:– CCT +37K– Duv +0.0016
2900K 2950K 3000K 3050K 3100K
-0.004
-0.002
0
0.002
0.004
CCT
Duv
5 Year Field Implementation Evaluation
• Replaced Luminaires after 5 years (2011 – 2016)
• Re-measured the modules and compared to new
• Color shift after 5 years:
– 20-30K
– 0.00056 – 0.00063Duv
St John’s BlackheathFixtures Mike Stoane Lighting
Good Product Design and Process Control
• Provides accurate colors when new
– Within 1x2McAdam
• Keeps colors stable over time
• Enables color warranty
• Enables color stability projections in terms of B0
– B for part of population outside spec
– 0 for no parts out of spec
Recommended specification for color consistency over time:
Must be based on B0LED Module supplier must provide color warranty
Color shift after 50,000h < 3McAdam Ellipse
Step 2: Accurate Testing - Problem
• Problem: standard LED production
testers and procedures not accurate
enough
• Example: LED manufacturer lists +/-
0.007 (x,y)
• Standard tester accuracy alone is far
outside green zone and even into the red-
zone– Not fit for critical (and non-critical)
illumination!
2800 2900 3000 3100 3200
-0.006
-0.004
-0.002
0
0.002
0.004
0.006
LED Manufacturer +/- 0.007 x,y
CCT
duv
Step 2: Accurate Testing – Problem Fixed
• NIST characterizes references sources with
sufficient (great!) accuracy
• With careful testing and procedures, sufficient
testing consistency can be achieved
– CCT: ~ +/- 20k
– Duv: ~ +/- 0.0005
– 10x better capability in Duv and CCT!2800 2900 3000 3100 3200
-0.006
-0.004
-0.002
0
0.002
0.004
0.006
NISTLED Manufacturer +/- 0.007 x,yImproved Tester
CCT
duv
Recommended specification for tester consistency:
CCT < +/- 20CCTDuv < +/- 0.005
Step 3: Improved Calculation of Data (Colorimetry)
• Color calculations done with Color Matching
Functions (CMFs)
• Standard color matching functions can give
inaccurate results
– Two sources have the same test result, but
appear different
• Can be fixed with improved CMFs
– Schanda, Csuti, Harbers - 2011
Can we Make Testing and Calculations Perfect?
• Testing and color quantification done based on “standard observers”
• Many proof-points that we see color similarly, but not the same
Victoria & Albert Museum, LondonDHA DesignsMike Stoane Lighting