New Color Quality Design for Attractive Lighting - Schedschd.ws/hosted_files/ialdenlightenamericas2015/56/New Color Quality... · New Color Quality Design for Lighting ... IALD Enlighten

New Color Quality Design for Lighting

– How lighting can be made more attractive?

Yoshi Ohno

Ph. D., NIST Fellow, Sensor Science Division

(IES Fellow, CIE President)

National Institute of Standards and Technology

Gaithersburg, Maryland USA

IALD Enlighten Americas 2015, Baltimore,

Oct. 8 to 10, 2015

National Institute of Standards and Technology (NIST)

Gaithersburg, Maryland campus

• National metrology institute for USA

under U.S. Dept. of Commerce

• NBS established in 1901, name changed to

NIST in 1988

• ~3000 researchers and staff in Gaithersburg.

• Annual budget ~$800M

3 IALD Enlighten Americas 2015

Color Quality = CCT and CRI ?

CCT: Correlated Color Temperature (CIE 15, CIE S017 ILV)

CRI: Color Rendering Index (CIE 13.3)

Some example

CCT = 3049 K

CRI (Ra)= 91

This product is not acceptable.

Why?

Too yellowish! (Duv= 0.012)

Normal CCT does not tell the whole story of chromaticity.


CCT=4000 K CCT=4000 K

CRI Ra=94 CRI Ra=78

This looks better

(for most people)

Color Quality = CCT and CRI ?

CRI does not tell the whole story of

color rendering.


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


Traditional White Light Chromaticity for Lighting

CIE 1931 (x, y) Diagram

ANSI C78.376-2001 for

fluorescent lamps IEC 60081 for Fluorescent Lamps


ANSI C78.377 (for Solid State Lighting Products)

(2015 rev)


Chromaticity shift across Planckian Locus

Lights below Planckian

locus look better.

Anecdotes say …

An example in neodymium

lamp


Duv defined in ANSI C78.377 (2008)

Symbol: Duv Closest distance from the Planckian locus on the (u', 2/3 v') diagram, with +

sign for above and - sign for below the Planckian locus.

Duv scale on (u’, v’) diagram


Recent study on white light perception by LRC

M. S. Rea,* J. P. Freyssinier, White Lighting, Volume 38, Number 2, 2013

• Viewed the white booth

with no objects inside

• Viewed immediately after

light was presented (no-

adaptation).

• Viewed after 45 sec.

(adaptation)


NIST Spectrally Tunable Lighting Facility



6 Duv points at each

CCT,

4 CCTs,

at total 23 points.

Total 50 spectra used.

• Real interior room setting with NIST STLF

at ~ 300 lx. (off-white walls)

• 18 subjects (20 to 70 yrs old)

• Viewed fruits/vegetables on the table,

his/her skin tone and the whole room.

• Judged which light is “more natural”.

2013 Vision Experiment at NIST

on Preferred and Acceptable level of Duv


Light spectra


• 5 min adaptation at

first point (each CCT)

• Ask “Is this light

acceptable?”

• Pair of light “A”, “B”

presented for 3 sec,

repeated.

• Ask “Which light looks

more natural?

• 1 min adaptation at

next point.

• Forward and backward

directions

• Repeat the two runs.

3500 K

Experimental Procedures

“A”

“B”


Which light looks more natural?


Experimental Procedures

• 6 Duv points at each

CCT

• 2 directions for each

CCT

• 4 CCTs

• 2 repeated runs for

each condition

Total 16 runs,

96 comparisons of pairs

of lights per subject.

Took ~ 4 h per subject.

18 subjects.

Whole experiment took

one month.

2700 K

3500 K

4500 K

6500 K


-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

6500K 4500K 3500K 2700K

Du

v

CCT

AVERAGE

1001

1002

1003

1004

1005

1006

1007

1009

1010

1011

1013

1014

1015

1016

1017

1018

1019

Results of 2013 Experiment 50 % crossover points of Duv (all subjects)

Std.de

v.


Results of “Is this light acceptable?”

Y. Ohno and M. Fein, Vision Experiment on Acceptable and Preferred White

Light Chromaticity for Lighting, CIE x029:2014, pp. 192 – 199 (2014)

Duv ≈

-0.015

Results of 2013 Experiment Average crossover points of Duv


Additional experiments with brownish walls with 6 subjects


Discussion by M Wei & Kevin Houser

Leukos, April 2015 http://dx.doi.org/10.1080/15502724.2015.1029131

“We infer that the preference expressed by participants in the

studies by Dikel and others [2014] and Ohno and Fein

[2014] may not be solely related to chromaticity.”

“aspects of color rendition (that is, color fidelity and relative

gamut) may also influence preference.”

http://dx.doi.org/10.1080/15502724.2015.1029131

http://dx.doi.org/10.1080/15502724.2015.1029131


Color rendering characteristics at different Duv levels


2015 Experiment at NIST

Same conditions as 2013:

CCT: 2700 K, 3500 K, 4500

K, 6500 K

Duv: -0.03 to 0.02

with light pairs adjusted for

nearly equal Qg and chroma

of red/green samples.

Same procedures

(except no repeated runs)

21 subjects (19 to 68 years

old)

Subjects observed fruits/

vegetables, entire room, and

skin tone.

Subjects selected light that

looked “more natural”


Lights used in the 2013 experiment


2015 Experiment settings


Results of 2015 Experiment

2013 results 2015 results

No significant differences found.


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

CRI Ra=94 CRI Ra=78

• CRI is a color fidelity metric.

• CRI score does not correlate well with perception when chroma is

more saturated.

Plots of 15

CQS samples

on CIELAB

(a*,b*)

The size of

plotted area is

“Gamut area”

Test

light

Referenc

e

Color contrast enhanced


Gamut increased by LED sources

Negative

Duv RGB RGBA Hybrid


Color Quality Scale (CQS)

Score is decreased for the

full color difference (same

as CRI)

Ref Test

Ref Test

Score is not penalized for

increase of chroma.

(Score is decreased for hue and

lightness shifts)

with limit of DC*ab<10 (CQS 9.0)

n Saturation factor

Davis, W. & Ohno, Y., “Color Quality Scale,” Optical Engineering, Optical

Engineering 033602-1 March 2010/Vol. 49_3 (2010)


CQS is designed to improve CRI and to measure “perceived fidelity”

CQS is not a color preference metric.

<Saturated> <De-saturated>

Ra

Qa

How CQS works

Increase of chroma

not penalized


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*

DC*ab = -16

DC*ab = 16

2014 Vision Experiment at NIST on preferred chroma saturation level

• 20 subjects

• 3 CCTs (2700, 3500, 5000 K) +

Duv= -0.015 (3500 K only)

• 4 different kinds of targets


Spectra of light

Duv= 0, Ra=92

at DC=0

Duv= 0, Ra=94

at DC=0

Duv= 0, Ra=89

at DC=0

Ra=90

at DC=0

Experimental Conditions

Condition 1: mixed

fruits/vegetable and room Condition 2: Skin tone

Condition 3: Red

Fruits/Vegetables

Condition 4: Green

Fruits/Vegetables


A Pair of Light presented sequentially

One was always

neutral one (DC=0).

Each light was

called “A” and “B”

“A” and “B”

assigned randomly.

Each light presented

for a few seconds.

Light was switched

back and forth for a

few times as

necessary.


Which light looks better?


Average Results for all subjects, all CCTs

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

-16 -12 -8 -4 0 4 8 12 16Perc

en

t o

f P

art

icip

an

ts w

ho

pre

ferr

ed

P

oin

t Average Preference for DC

Average

Room

Skin

Green

Red

<Saturated> <De-saturated> Neutral

Y. Ohno, M. Fein, C. Miller, Vision Experiment on Chroma Saturation for

Color Quality Preference, CIE 216 :2015, pp. 60 – 69 (2015)

DCab

*


Expected Color Preference Scale

Preference reference

Illuminant

<Saturated> <De-saturated>

Fidelity reference

Illuminant


TC 1-90: Colour Fidelity Index

Chair: H. Yaguchi (JP)

Developing an updated color fidelity metric (for future

replacement of CRI).

TC 1-91: New Methods for Evaluating the Colour

Quality of White-Light Sources

Chair: Y. Lin (CN)

Developing a technical report on the studies on color qualities

other than color fidelity.

Two committees in CIE on Color Quality

CQS is included in TC 1-91 draft.

TC1-91 report will not recommend a color-preference metric.


From presentation by Michael Royer at Lightfair 2015

IES TM-30 IES Method for Evaluating Light

Source Color Rendition

New color fidelity metric (using 99 test samples)

Relative gamut area

High CRI

sources do not

have much

design flexibility


Summary

More preferred lights exist outside current standards. CRI

unduly penalizes preferred lights.

Lights with chromaticity below Planckian locus (Duv≈ -0.015)

are generally preferred (in all CCT ranges).

ANSI C78.377 WG is considering adding “perception-based”

chromaticity specifications.

Lights with slightly saturated chroma (peak at DC*ab ≈ 5) are

generally preferred. De-saturating lights are not preferred.

A color-preference metric is needed (in addition to color

fidelity metric). Such a work should start in CIE.

Verification of these effects in real applications is desired.


THANK YOU for your

attention.

Contact: Yoshi Ohno

[email protected]

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