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 –
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Traditional White Light Chromaticities for Lighting
CIE 1931 (x, y) Diagram
ANSI C78.376‐2001 for fluorescent lamps IEC 60081 for Fluorescent Lamps
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ANSI C78.377-2011 (for Solid State Lighting Products)
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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
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Uncertainty of measurement of Duv : ~ 0.001 (k=2)
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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.
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Light spectra
Qa=97
Qa=96
Qa=96
Qa=95
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20
Experimental Design
18 subjects (all having normal color vision)
711
Ages ranging from…
19 years old 70 years old
7030 40 50 60
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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.
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Fresh fruits and vegetables on the table (replaced every one to three days)
Apple (red) OrangeApple (pale red) Green pepperOrange lettuceBanana StrawberryTomato grapes
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Preparation for each subject
• Ishihara Test for normal color vision
• Explanations on experiment
• Instructions (questions, use of mouse)
• Trial run
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• 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
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• 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
“Is this light acceptable or not?”
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• 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
Pair of lights switched every 3 seconds
Question: “Which light looks more natural?”
Subject clicked the mouse when more natural light is presented.
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• 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
Pair of lights switched every 3 seconds
Question: “Which light looks more natural?”
Subject clicked the mouse when more natural light is presented.
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Which light looks more natural?
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Which light looks more natural?
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• 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
Pair of lights switched every 3 seconds
Question: “Which light looks more natural?”
Subject clicked the mouse when more natural light is presented.
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• 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
Pair of lights switched every 3 seconds
Question: “Which light looks more natural?”
Subject clicked the mouse when more natural light is presented.
“Is this light acceptable or not?”
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• 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
Pair of lights switched every 3 seconds
Question: “Which light looks more natural?”
Subject clicked the mouse when more natural light is presented.
Pair of lights switched every 3 seconds
Question: “Which light looks more natural?”
Subject clicked the mouse when more natural light is presented.
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• 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
Pair of lights switched every 3 seconds
Question: “Which light looks more natural?”
Subject clicked the mouse when more natural light is presented.
Pair of lights switched every 3 seconds
Question: “Which light looks more natural?”
Subject clicked the mouse when more natural light is presented.
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• 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
Pair of lights switched every 3 seconds
Question: “Which light looks more natural?”
Subject clicked the mouse when more natural light is presented.
Pair of lights switched every 3 seconds
Question: “Which light looks more natural?”
Subject clicked the mouse when more natural light is presented.
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• 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
Pair of lights switched every 3 seconds
Question: “Which light looks more natural?”
Subject clicked the mouse when more natural light is presented.
Pair of lights switched every 3 seconds
Question: “Which light looks more natural?”
Subject clicked the mouse when more natural light is presented.
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• 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
Pair of lights switched every 3 seconds
Question: “Which light looks more natural?”
Subject clicked the mouse when more natural light is presented.
Pair of lights switched every 3 seconds
Question: “Which light looks more natural?”
Subject clicked the mouse when more natural light is presented.
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.
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In addition, six subjects repeated experiments with brownish walls identically furnished.
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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
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‐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
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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
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‐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)
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‐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.
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Plotted on ANSI C78.377
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Results of “Is this light acceptable or not?”
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Color rendering characteristics
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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]