"Vision Experiment on White Light Chromaticity for Lighting," Yoshi

1CIE/USA-CNC/CIE 2013

CIE/USA-CNC/CIE Biennial Joint Meeting, Davis, CA, Nov. 7-8, 2013

Yoshi Ohno*1 and Mira Fein*21 National Institute of Standards and Technology, Gaithersburg, Maryland, USA

Ph. D., NIST Fellow, IESNA Fellow, CIE VP‐Technical2 Psychology Department, Oberlin College, Oberlin, Ohio, USANIST Guest Researcher under NIST Summer Undergraduate Research Fellowship Program

Vision Experiment on White Light Chromaticity for Lighting

– Duv levels Perceived Most Natural –


Traditional White Light Chromaticities for Lighting

CIE 1931 (x, y) Diagram

ANSI C78.376‐2001 for fluorescent lamps IEC 60081 for Fluorescent Lamps


ANSI C78.377-2011 (for Solid State Lighting Products)

4A*STAR NMC Seminar

Chromaticity shift across Planckian Locus

Lights below Planckianlocus look better.

Anecdotes say …

An example in neodymium lamp

5A*STAR NMC Seminar

Recent Study on white light perception by LRC

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

• 20 observers• Viewed the white box immediately after light was shown.

• Viewed after 45 sec. (adaptation for each light)

• No adaptation (only 4 sec. closing eyes) before immediate viewing of next light. (subject was adapted to previous light?)

6A*STAR NMC Seminar

Duv defined in ANSI C78.377

+ Duv

- Duv

Symbol: DuvClosest 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

7A*STAR NMC Seminar

NIST Spectrally Tunable Lighting Facility

8A*STAR NMC Seminar

NIST Spectrally Tunable Lighting Facility


Uncertainty of measurement of Duv : ~ 0.001 (k=2)


3500 K

Experimental Design

4500 K

6500 K

2700 K

Experiments prepared for 4 CCTs, at 6 Duv points at each CCT, at total 23 points.

Spectra prepared for the 23 points plus points in between and outside, total 50points.


Light spectra

Qa=97

Qa=96

Qa=96

Qa=95


20

Experimental Design

18 subjects (all having normal color vision)

711

Ages ranging from…

19 years old 70 years old

7030 40 50 60


Experimental Setting

• Room was set with neutral light‐gray walls (for main experiment)• Illuminance ~300 lx on the table (variations within ±1 %).• Subjects viewed fruits on the table, his/her face skin tone in mirror and the whole room.


Fresh fruits and vegetables on the table (replaced every one to three days)

Apple (red) OrangeApple (pale red) Green pepperOrange lettuceBanana StrawberryTomato grapes


Preparation for each subject

• Ishihara Test for normal color vision

• Explanations on experiment

• Instructions (questions, use of mouse)

• Trial run


• 6 Duv points at each run for one CCT

• 2 directions for each CCT

• 4 CCTs• 2 repeated runs for

each condition

3500 K

Experimental Procedures





each condition

3500 K


“Is this light acceptable or not?”





each condition

3500 K


Pair of lights switched every 3 seconds

Question: “Which light looks more natural?”

Subject clicked the mouse when more natural light is presented.





each condition

3500 K






Which light looks more natural?





each condition

3500 K









each condition

3500 K





“Is this light acceptable or not?”





each condition

3500 K












each condition

3500 K








Total 16 runs, 92 comparisons of pairs of light per subject.

Took ~ 4 h per subject.

Subjects chose one half‐day session or two 2 h sessions on different dates.


In addition, six subjects repeated experiments with brownish walls identically furnished.


Raw Data(for each subject)

“0” higher Duv chosen

‐0.03 ‐0.02 ‐0.01 0.00 0.01 0.02

2700K backward 0 1 1 1 1 1

2700K forward 0 0 0 1 1 1

2700K backward 0 1 1 1 1 1

2700K forward 0 0 0 0 1 1

Average 0 0.5 0.5 0.75 1 1

“1” lower Duv chosen


‐0.03 ‐0.02 ‐0.01 0.00 0.01 0.02

2700K backward 0 1 1 1 1 1

2700K forward 0 0 0 1 1 1

2700K backward 0 1 1 1 1 1

2700K forward 0 0 0 0 1 1

Average 0 0.5 0.5 0.75 1 1

3500K forward 0 0 1 1 1 1

3500K backward 0 0 1 1 1 1

3500K forward 0 0 0 1 1 1

3500K backward 0 0 0 1 1 1

Average 0 0 0.5 1 1 1

4500K backward 0 1 1 1 1 1

4500K forward 0 0 0 1 1 1

4500K backward 0 1 1 1 1 1

4500K forward 0 0 0 1 1 0

Average 0 0.5 0.5 1 1 0.75

6500K forward 0 1 1 1 1 1

6500K backward 0 1 1 1 1 1

6500K forward 0 0 1 1 1 1

6500K backward 1 1 1 1 1 1

Average 0.25 0.75 1 1 1 1

Plotting data(for each subject)

00.10.20.30.40.50.60.70.80.91

‐0.03 ‐0.02 ‐0.01 0 0.01

Ratio

of N

egative Duv

Cho

sen

Duv

2700K

50 % crossover point


00.10.20.30.40.50.60.70.80.91

‐0.03 ‐0.02 ‐0.01 0 0.01

Ratio

of N

egative Duv

Cho

sen

Duv

2700K

0

0.2

0.4

0.6

0.8

1

‐0.03 ‐0.02 ‐0.01 0 0.01 0.02Ratio

of N

egative Duv

Cho

sen

Duv

Data Example (one subject)

3500 K

0

0.2

0.4

0.6

0.8

1

‐0.03 ‐0.02 ‐0.01 0 0.01 0.02Ratio

of N

egative Duv

Cho

sen

Duv

4500 K

0

0.2

0.4

0.6

0.8

1

‐0.03 ‐0.02 ‐0.01 0 0.01 0.02

Ratio

of N

egative Duv

Cho

sen

Duv

6500 K


‐0.04

‐0.03

‐0.02

‐0.01

0

0.01

0.02

0.03

0.04

6500 4500 3500 2700

Duv

CCT (K)

50 % crossover points of Duv (one subject)


‐0.04

‐0.03

‐0.02

‐0.01

0

0.01

0.02

0.03

0.04

6500K 4500K 3500K 2700K

Duv

CCT

AVERAGE10011002100310041005100610071009101010111013101410151016101710181019

50 % crossover points of Duv (all subjects)

Std.dev.


Plotted on ANSI C78.377


Results of “Is this light acceptable or not?”


Color rendering characteristics


Conclusions• The chromaticity region below the Planckian Locus (Duv around ‐

0.015) seems to be well preferred over white light on the Planckian locus for typical indoor applications.

• Results are similar at all CCTs (2700 K to 6500 K) – different from the LRC results.

• Higher “unacceptable” rating at positive Duv at lower CCTs.

• Effects of brown wall was insignificant.

• Further experiments or observations with real application scenes are desired.

We thank DOE for their support of this research.Thanks are also due to Dr. Podobedov at NIST who developed the

control program for the experiment.

THANK YOU FOR YOUR ATTENTION. Contact: [email protected]

"Vision Experiment on White Light Chromaticity for Lighting," Yoshi

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