7. Ohno Chromaticity Specifications and Colour - … Annex Conference; 23 November 2017 1...

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


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


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)


Duv defined in

ANSI C78.377

ANSI C78.377


Specifications expressed in (x, y) or (u’,v’)

(u’, v’) diagram is recommended


Annex C. 4-step u’v’ circlesAnnex B. 4-step quadrangles

Annex B, C for Smaller Tolerances


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


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


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


• 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)


ANCI C78.377-2017 revision published, July, 2017

Extended

Specification

Basic Specification

Flexible Duv Specification


Some Products already available

Wouter Soer, presentation at DOE SSL R&D Workshop Jan. 2017


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


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


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).


� 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”


“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


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


Which light looks better? A

CRI Ra=94

Which light looks better? AWhich light looks better? B

CRI Ra=78


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)


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


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


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


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


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.


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


Thank You – Any Questions

Contact:

Yoshi Ohno

[email protected]

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7. Ohno Chromaticity Specifications and Colour - … Annex Conference; 23 November 2017 1...

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