Vision Experiment on White Light Chromaticity for Lighting Duv levels Perceived Most Natural

Transcription

1 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 1

2 Traditional White Light Chromaticities for Lighting ANSI C for fluorescent lamps IEC for Fluorescent Lamps CIE 1931 (x, y) Diagram 2

3 ANSI C (for Solid State Lighting Products) 3

4 Chromaticity shift across Planckian Locus Anecdotes say Lights below Planckian locus look better. An example in neodymium lamp A*STAR NMC Seminar 4

5 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

6 Duv defined in ANSI C Closest Symbol: distance D from the Planckian locus on the (u', 2/3 v') diagram, with + uv sign for above and - sign for below the Planckian locus. Duv scale on (u, v ) diagram + Duv -Duv A*STAR NMC Seminar 6

7 NIST Spectrally Tunable Lighting Facility A*STAR NMC Seminar 7

8 NIST Spectrally Tunable Lighting Facility A*STAR NMC Seminar 8

9 9

10 Uncertainty of measurement of Duv : ~ (k=2) 10

11 Experimental Design 4500 K 3500 K 2700 K Experiments prepared for 4 CCTs, at 6 Duv points at each CCT, at total 23 points K Spectra prepared for the 23 points plus points in between and outside, total 50 points. 11

12 Light spectra Qa=97 Qa=96 Qa=96 Qa=95 12

13 Experimental Design 18 subjects (all having normal color vision) 11 7 Ages ranging from years old 70 years old 13

14 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. 14

15 Fresh fruits and vegetables on the table (replaced every one to three days) Apple (red) Apple (pale red) Orange Banana Tomato Orange Green pepper lettuce Strawberry grapes 15

16 Preparation for each subject Ishihara Test for normal color vision Explanations on experiment Instructions (questions, use of mouse) Trial run 16

17 Experimental Procedures 3500 K 6 Duv points at each run for one CCT 2 directions for each CCT 4 CCTs 2 repeated runs for each condition 17

18 Experimental Procedures 3500 K 6 Duv points at each run for one CCT 2 directions for each CCT 4 CCTs 2 repeated runs for each condition Is this light acceptable or not? 18

19 Experimental Procedures 3500 K 6 Duv points at each run for one CCT 2 directions for each CCT 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. 19

20 Experimental Procedures 3500 K 6 Duv points at each run for one CCT 2 directions for each CCT 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. 20

21 Which light looks more natural? 21

22 Which light looks more natural? 22

23 Experimental Procedures 3500 K 6 Duv points at each run for one CCT 2 directions for each CCT 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. 23

24 Experimental Procedures 3500 K 6 Duv points at each run for one CCT 2 directions for each CCT 4 CCTs 2 repeated runs for each condition Pair Is this of lights light switched every acceptable 3 seconds or not? Question: Which light looks more natural? Subject clicked the mouse when more natural light is presented. 24

25 Experimental Procedures 3500 K 6 Duv points at each run for one CCT 2 directions for each CCT 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. 25

26 Experimental Procedures 3500 K 6 Duv points at each run for one CCT 2 directions for each CCT 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. 26

27 Experimental Procedures 3500 K 6 Duv points at each run for one CCT 2 directions for each CCT 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. 27

28 Experimental Procedures 3500 K 6 Duv points at each run for one CCT 2 directions for each CCT 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. 28

29 Experimental Procedures 3500 K 6 Duv points at each run for one CCT 2 directions for each CCT 4 CCTs 2 repeated runs for each condition Pair Total of 16 lights runs, switched 92 every comparisons 3 seconds of pairs of light per subject. Question: Which light looks Took more ~ 4 h per natural? subject. Subjects clicked chose the one half mouse day session when or more two 2 h natural sessions light on different is presented. dates. 29

30 In addition, six subjects repeated experiments with brownish walls identically furnished. 30

31 Raw Data (for each subject) K backward K forward K backward K forward Average higher Duv chosen 1 lower Duv chosen 31

32 Plotting data (for each subject) K backward K forward K backward K forward Average K forward K backward K forward K backward Average K backward K forward K backward K forward Average K forward K backward K forward K backward Average Ratio of Negative Duv Chosen K Duv 50 % crossover point 32

33 Data Example (one subject) Ratio of Negative Duv Chosen K Duv Ratio of Negative Duv Chosen K Duv Ratio of Negative Duv Chosen K Duv Ratio of Negative Duv Chosen K Duv 33

34 50 % crossover points of Duv (one subject) Duv CCT (K) 34

35 50 % crossover points of Duv (all subjects) Duv Std.dev. 6500K 4500K 3500K 2700K CCT AVERAGE

36 Plotted on ANSI C

37 Results of Is this light acceptable or not? 37

38 Color rendering characteristics 38

39 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: ohno@nist.gov 39