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Vision Experiment on White Light Chromaticity for Lighting –Duv Levels Perceived Most Natural – CIE/USA-CNC/CIE Biennial Joint Meeting, Davis, CA, Nov. 7-8, 2013 Vision Experiment on White Light Chromaticity for Lighting –Duv levels Perceived Most Natural – Yoshi Ohno*1 and Mira Fein*2 1 National Institute of Standards and Technology, Gaithersburg, Maryland, USA Ph. D., NIST Fellow, IESNA Fellow, CIE VP‐Technical 2 Psychology Department, Oberlin College, Oberlin, Ohio, USA NIST Guest Researcher under NIST Summer Undergraduate Research Fellowship Program CIE/USA-CNC/CIE 2013 1 Traditional White Light Chromaticities for Lighting ANSI C78.376‐2001 for fluorescent lamps IEC 60081 for Fluorescent Lamps CIE 1931 (x, y) Diagram CIE/USA-CNC/CIE 2013 2 ANSI C78.377-2011 (for Solid State Lighting Products) CIE/USA-CNC/CIE 2013 3 Chromaticity shift across Planckian Locus Anecdotes say … Lights below Planckian locus look better. An example in neodymium lamp A*STAR NMC Seminar 4 Recent Study on white light perception by LRC • 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?) M. S. Rea,* J. P. Freyssinier, White Lighting, Volume 38, Number 2, April 2013 A*STAR NMC Seminar 5 Duv defined in ANSI C78.377 Closest distance from the Planckian locus on the (u', 2/3 v') diagram, with + Symbol: Duv sign for above and - sign for below the Planckian locus. Duv scale on (u’, v’) diagram + Duv -Duv A*STAR NMC Seminar 6 NIST Spectrally Tunable Lighting Facility A*STAR NMC Seminar 7 NIST Spectrally Tunable Lighting Facility A*STAR NMC Seminar 8 CIE/USA-CNC/CIE 2013 9 Uncertainty of measurement of Duv : ~ 0.001 (k=2) CIE/USA-CNC/CIE 2013 10 Experimental Design Experiments prepared for 4 CCTs, 2700 K at 6 Duv points at 3500 K each CCT, at total 23 points. 4500 K Spectra prepared for the 23 points plus 6500 K points in between and outside, total 50 points. CIE/USA-CNC/CIE 2013 11 Light spectra Qa=97 Qa=96 Qa=96 Qa=95 CIE/USA-CNC/CIE 2013 12 Experimental Design 18 subjects (all having normal color vision) 11 7 Ages ranging from… 20 30 40 50 60 70 19 years old 70 years old CIE/USA-CNC/CIE 2013 13 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. CIE/USA-CNC/CIE 2013 14 Fresh fruits and vegetables on the table (replaced every one to three days) Apple (red) Orange Apple (pale red) Green pepper Orange lettuce Banana Strawberry Tomato grapes CIE/USA-CNC/CIE 2013 15 Preparation for each subject • Ishihara Test for normal color vision • Explanations on experiment • Instructions (questions, use of mouse) • Trial run CIE/USA-CNC/CIE 2013 16 Experimental Procedures • 6 Duv points at each run for one CCT • 2 directions for each CCT 3500 K • 4 CCTs • 2 repeated runs for each condition CIE/USA-CNC/CIE 2013 17 Experimental Procedures • 6 Duv points at each run for one CCT • 2 directions for each CCT 3500 K • 4 CCTs • 2 repeated runs for each condition “Is this light acceptable or not?” CIE/USA-CNC/CIE 2013 18 Experimental Procedures • 6 Duv points at each run for one CCT • 2 directions for each CCT 3500 K • 4 CCTs • 2 repeated runs for each condition Pair of lights switched every 3 seconds Question: “Which light looks more natural?” Subject clicked the mouse when more natural light is presented. CIE/USA-CNC/CIE 2013 19 Experimental Procedures • 6 Duv points at each run for one CCT • 2 directions for each CCT 3500 K • 4 CCTs • 2 repeated runs for each condition Pair of lights switched every 3 seconds Question: “Which light looks more natural?” Subject clicked the mouse when more natural light is presented. CIE/USA-CNC/CIE 2013 20 Which light looks more natural? CIE/USA-CNC/CIE 2013 21 Which light looks more natural? CIE/USA-CNC/CIE 2013 22 Experimental Procedures • 6 Duv points at each run for one CCT • 2 directions for each CCT 3500 K • 4 CCTs • 2 repeated runs for each condition Pair of lights switched every 3 seconds Question: “Which light looks more natural?” Subject clicked the mouse when more natural light is presented. CIE/USA-CNC/CIE 2013 23 Experimental Procedures • 6 Duv points at each run for one CCT • 2 directions for each CCT 3500 K • 4 CCTs • 2 repeated runs for each condition Pair“Is thisof lights light switched everyacceptable 3 seconds or not?” Question: “Which light looks more natural?” Subject clicked the mouse when more natural light is presented. CIE/USA-CNC/CIE 2013 24 Experimental Procedures • 6 Duv points at each run for one CCT • 2 directions for each CCT 3500 K • 4 CCTs • 2 repeated runs for each condition Pair of lights switched every 3 seconds Question: “Which light looks more natural?” Subject clicked the mouse when more natural light is presented. CIE/USA-CNC/CIE 2013 25 Experimental Procedures • 6 Duv points at each run for one CCT • 2 directions for each CCT 3500 K • 4 CCTs • 2 repeated runs for each condition Pair of lights switched every 3 seconds Question: “Which light looks more natural?” Subject clicked the mouse when more natural light is presented. CIE/USA-CNC/CIE 2013 26 Experimental Procedures • 6 Duv points at each run for one CCT • 2 directions for each CCT 3500 K • 4 CCTs • 2 repeated runs for each condition Pair of lights switched every 3 seconds Question: “Which light looks more natural?” Subject clicked the mouse when more natural light is presented. CIE/USA-CNC/CIE 2013 27 Experimental Procedures • 6 Duv points at each run for one CCT • 2 directions for each CCT 3500 K • 4 CCTs • 2 repeated runs for each condition Pair of lights switched every 3 seconds Question: “Which light looks more natural?” Subject clicked the mouse when more natural light is presented. CIE/USA-CNC/CIE 2013 28 Experimental Procedures • 6 Duv points at each run for one CCT • 2 directions for each CCT 3500 K • 4 CCTs • 2 repeated runs for each condition PairTotal of 16 lights runs switched, 92 everycomparisons 3 secondsof pairs of light per subject. Question: “Which light looksTook more~ 4 h pernatural?” subject. SubjectSubjects clicked chose the one half‐ mouseday session when or more two 2 h naturalsessions light on differentis presented. dates. CIE/USA-CNC/CIE 2013 29 In addition, six subjects repeated experiments with brownish walls identically furnished. CIE/USA-CNC/CIE 2013 30 Raw Data (for each subject) ‐0.03 ‐0.02 ‐0.01 0.00 0.01 0.02 2700K backward011111 2700K forward000111 2700K backward011111 2700K forward000011 Average 0 0.5 0.5 0.75 1 1 “0” higher Duv chosen “1” lower Duv chosen CIE/USA-CNC/CIE 2013 31 Plotting data (for each subject) ‐0.03 ‐0.02 ‐0.01 0.00 0.01 0.02 2700K backward011111 2700K forward 000111 2700K backward011111 2700K forward 000011 Average 0 0.5 0.5 0.75 1 1 2700K 3500K forward 001111 1 3500K backward001111 Chosen 0.9 3500K forward 000111 0.8 Duv 3500K backward000111 0.7 Average 000.5111 0.6 4500K backward011111 Negative 0.5 4500K forward 000111 of 0.4 4500K backward011111 0.3 4500K forward 000110 Ratio 0.2 Average 0 0.5 0.5 1 1 0.75 0.1 6500K forward 011111 0 6500K backward011111 ‐0.03 ‐0.02 ‐0.01 0 0.01 6500K forward 001111 Duv 6500K backward111111 Average 0.25 0.75 1 1 1 1 50 % crossover point CIE/USA-CNC/CIE 2013 32 Data Example (one subject) 1 1 0.9 2700K Chosen 0.8 0.8 4500 K Chosen Duv 0.7 0.6 0.6 Duv 0.5 Negative 0.4 0.4 of 0.3 Negative 0.2 0.2 Ratio of 0.1 0 0 ‐0.03 ‐0.02 ‐0.01 0 0.01 Ratio ‐0.03 ‐0.02 ‐0.01 0 0.01 0.02 Duv Duv 1 1 3500 K 6500 K 0.8 0.8 Chosen Chosen 0.6 Duv 0.6 Duv 0.4 0.4 Negative Negative 0.2 0.2 of of 0 0 Ratio Ratio ‐0.03 ‐0.02 ‐0.01 0 0.01 0.02 ‐0.03 ‐0.02 ‐0.01 0 0.01 0.02 Duv Duv CIE/USA-CNC/CIE 2013 33 50 % crossover points of Duv (one subject) 0.04 0.03 0.02 0.01 0 Duv ‐0.01 ‐0.02 ‐0.03 ‐0.04 6500 4500 3500 2700 CCT (K) CIE/USA-CNC/CIE 2013 34 50 % crossover points of Duv (all subjects) 0.04 AVERAGE 1001 0.03 1002 1003 0.02 1004 1005 0.01 1006 Std.dev 1007 0 . 1009 Duv 1010 ‐0.01 1011 1013 ‐0.02 1014 1015 ‐0.03 1016 1017 ‐0.04 1018 6500K 4500K 3500K 2700K 1019 CCT CIE/USA-CNC/CIE 2013 35 Plotted on ANSI C78.377 CIE/USA-CNC/CIE 2013 36 Results of “Is this light acceptable or not?” CIE/USA-CNC/CIE 2013 37 Color rendering characteristics CIE/USA-CNC/CIE 2013 38 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.
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