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SSL Annex Conference; 23 November 2017 1
ssl.iea-4e.org
Yoshi Ohno
SSL Annex IC 2017 Task Leader
(CIE President, NIST Fellow)National Institute of Standards and Technology, USA
SSL Annex Conference; 23 November 2017 2
Color Quality of Lighting
Chromaticity (white light)
Color Rendering
Color Quality
400 450 500 550 600 650 700
400 500 600 700
• CCT, Duv
• Chromaticity
coordinates
(x,y), (u’,v’)
• Color fidelity (CRI)
• Color preference
SSL Annex Conference; 23 November 2017 3
Standards for White Light Chromaticity for SSL
IEC 60081 for Fluorescent
Lamps (5 step MacAdam
ellipses)
ANSI C78.377-2015 Chromaticity Specifications for Solid State
Lighting Products
1st version 2008
(Ohno, Technical coordinator)
SSL Annex Conference; 23 November 2017 4
Duv defined in
ANSI C78.377
ANSI C78.377
SSL Annex Conference; 23 November 2017 5
Specifications expressed in (x, y) or (u’,v’)
(u’, v’) diagram is recommended
SSL Annex Conference; 23 November 2017 6
Annex C. 4-step u’v’ circlesAnnex B. 4-step quadrangles
Annex B, C for Smaller Tolerances
SSL Annex Conference; 23 November 2017 7
n-step u’v’ circle: u’v’ circle with
a radius n x 0.0011.
( This corresponds to n-step
MacAdam ellipses.)
5-step u’v’ circles for
IEC 60081
CIE TN 001 Chromaticity Difference SpecificationPublished in July 2014
u’v’ circle: a circle with radius r on
CIE (u’,v’) diagram.
CIE TN 001: Freely available on CIE website:
Google “TN 001”
u’v’ circle is recommended to
replace MacAdam ellipses
• Requires 3 parameters
• No standards for interpolation
• Research by 1 subject
SSL Annex Conference; 23 November 2017 8
Preference to below blackbody
Ra score does not
correspond well with
visual evaluation.
CRI Ra = 77
An example of a
neodymium lamp
Above blackbody
Below blackbody
SSL Annex Conference; 23 November 2017 9
Recent Studies
Experiment on
perceived white point
by LRC (2013)
Experiment on preferred
lighting by NRC, Canada
(2013)
NIST vision experiment
in 2013 & 2015
Dikel et al, ”Preferred Chromaticity of Color-
Tunable LED Lighting”, LEUKOS, 10:2, 101-
115, DOI: 10.1080/15502724.2013.855614
(2013).
Ohno, Y., Fein, M., Vision Experiment on
Acceptable and Preferred White Light
Chromaticity for Lighting, CIE x039:2014,
pp. 192-199 (2014).
M. S. Rea,* J. P. Freyssinier, “White
Lighting”, CR&A, 30-2, 82-92, 2013.
10Energy Star Webinar March 2016
NIST Spectrally Tunable Lighting Facility
SSL Annex Conference; 23 November 2017 11
• 18 subject (2013), 21 subjects (2015).
• Targets: (1) mixed fruits and vegetables
and the whole room, (2) skin tone.
• 23 pairs of light presented.
• Subjects adapted to each Duv point.
• Asked which light looks “more natural”
NIST Experiments on Preferred and Acceptable level of Duv
(2013, 2015)
Duv ≈
-0.015
Ohno, Y., Fein, M., Vision Experiment on Acceptable and Preferred White Light
Chromaticity for Lighting, CIE x039:2014, pp. 192-199 (2014).
Ohno, Y., Oh, Semin., Vision Experiment II on White Light Chromaticity
for Lighting, CIE x042:2016, pp. 175-184 (2016)
SSL Annex Conference; 23 November 2017 1212
ANCI C78.377-2017 revision published, July, 2017
Extended
Specification
Basic Specification
Flexible Duv Specification
SSL Annex Conference; 23 November 2017 13
Some Products already available
Wouter Soer, presentation at DOE SSL R&D Workshop Jan. 2017
SSL Annex Conference; 23 November 2017 14
Color Quality of Lighting
Chromaticity (white light)
Color Rendering
Color Quality
400 450 500 550 600 650 700
400 500 600 700
• CCT, Duv
• Chromaticity
coordinates
(x,y), (u’,v’)
• Color fidelity (CRI)
• Color preference
SSL Annex Conference; 23 November 2017 15
Color quality is the most critical characteristic for lighting
quality.
Color Rendering Index – CRI (CIE 13.3:1995) – with
1974 formula, has been used over 40 years.
Measure for Color Quality of Light
Sources for General Lighting
SSL Annex Conference; 23 November 2017 16
Problems of CRI with SSL Sources
• CRI worked well for traditional lamps (FLs).
• LEDs (SSL) emerged.
• CRI (Ra) values do not always correlate
well with visual evaluation.
• CRI is used in products specifications, many
government programs, energy regulations, etc.
• General trade-off relationship, CRI vs lm/W.
(CRI is an energy-related issue)
• Many proposals to improve CRI (e.g., CQS).
SSL Annex Conference; 23 November 2017 17
� Published April 2017, from TC1-90.
� First CIE publication on a metric of color
rendering since 1974 (CIE 13.2). CIE 13.3
(1995) is only editorial revision.
� This is based on Fidelity Index Rf in IES TM-30,
color space and all formulae updated.
� New design tool for various applications.
CIE 224: CIE 2017 Colour Fidelity Index for Accurate Scientific Use
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
400 450 500 550 600 650 700
Re
fle
cta
nce
fa
cto
r
Wavelength (nm)
� “The colour fidelity index Rf is not a
replacement of the CRI (Ra) for the
purpose of rating and specification of
products nor for regulatory or other minimum performance requirements”
SSL Annex Conference; 23 November 2017 18
“Color Fidelity”
Reference illuminantTest sourcePlanckian
(CCT<5000 K) Standard Daylight
(CCT > 5000 K)
Same CCT [K]
CRI Ra, R9, ..
CIE 2017 Rf
TM-30 Rf
Color Fidelity: How accurate the
object colors appear compared
to the reference illuminant
SSL Annex Conference; 23 November 2017 19
Two Aspects in the Problems of CRI
• Outdated color space (W*U*V*)
• Outdated chromatic adaptation transform
• Too small number (8) of test samples
1. Scientific inaccuracies as a color fidelity metric
2. Problem of CRI being a color fidelity metric
• Perception of color quality is different from color fidelity
• Consider color preference
The users of lighting expect CRI to work
as an overall color quality measure.
Addressed
by CIE 224Color fidelity is a fundamental measure of
color quality
Not yet
addressed
SSL Annex Conference; 23 November 2017 20
Which light looks better? A
CRI Ra=94
Which light looks better? AWhich light looks better? B
CRI Ra=78
SSL Annex Conference; 23 November 2017 21
Why perception differs from the CRI scores?
Test light
(Ra=78)
Reference
(Planckian)
CRI Ra=78 CRI Ra=94
• Increased color contrast is preferred.
• CRI penalizes good preferred light sources.
Looks better (for most people)
SSL Annex Conference; 23 November 2017 22
Most saturated
Most de-saturated-80
-60
-40
-20
0
20
40
60
80
100
-80 -60 -40 -20 0 20 40 60 80
a*
CIELAB
b*
∆C*ab = -16
∆C*ab = 16
2014 Vision Experiment at NISTon preferred chroma saturation level
• 20 subjects
• 2700 K, 3500 K, 5000 K
• Duv=0, -0.015 (3500 K only)
• Illuminance 300 lx
SSL Annex Conference; 23 November 2017 23
0%
20%
40%
60%
80%
100%
-16 -12 -8 -4 0 4 8 12 16
Subjects' preference
Chroma difference ∆∆∆∆C*ab (CQS red sample)
Fruits/Vegetable
Skin tone
Red fruits
Green fruits
Y. Ohno, M. Fein, C. Miller, Vision Experiment on Chroma Saturation
for Color Quality Preference, CIE 216 :2015, pp. 60 – 69 (2015)
Mixed fruits & v.
Skin tone
Red fruits/vegetables
Green fruits/vegetables
Results of 2014 experiment
Average of all CCTs
Over-saturation
De-saturationCRI Ra
100
90
80
70
60
50
Don’t raise the bar for CRI too high.
Use additional metric to improve color quality
SSL Annex Conference; 23 November 2017 24
Image from
Michael Royer
IES TM-30 Concept of a Two-Metric System (2015)
Gamut
Rg
Fidelity RfImage from Michael Royer.
NIST
experiment
lights
∆C=8
∆C=4
SSL Annex Conference; 23 November 2017 25
Gamut area is not sufficient
IES Rg=100
CIE Rf=77
Different gamut shapes with same gamut area
Perceived color quality of these two lights are significantly different.
This looks better
IES Rg=100
CIE Rf=77
SSL Annex Conference; 23 November 2017 26
2016 NIST experiment on color saturation preference in different hues
11 different gamut shapes
19 subjects evaluate preference in light pairs
Y. Ohno, S. Oh, Y. Kwak, Vision Experiment on Chroma Saturation
Preference in Different Hues, Proc. CIE 2017 Midterm Jeju, Korea (2017)
(Numbers) are
∆C*ab from the
reference.
SSL Annex Conference; 23 November 2017 27
Summary
CRI Ra, R9
CIE 2017 Rf
IES TM-30 Rf
<Fidelity>
<Preference/perception>
.S used as design tools, research
SSS still used for general products
specifications, energy
regulations, etc.
Overall Color Quality
Color Fidelity
(CIE 224)
Color
perception/
preference
CRI
TM-30 Rg
GAI
CQS
and other metrics
Replace CRI
in the future
CIE is developing a standard
preference/perception metric
TC1-91� New TC
SSL Annex Conference; 23 November 2017 28
Thank You – Any Questions
Contact:
Yoshi Ohno