New Method for Evaluating Light Source Color Rendition (IES TM-30-15)

Transcription

1 New Method for Evaluating Light Source Color Rendition (IES TM-30-15) IES México XVII Seminario de Iluminación May 18, 2016 Kevin W. Houser, PhD, PE, FIES Professor of Architectural Engineering The Pennsylvania State University Editor-in-Chief LEUKOS, the journal of IES

2 Which do you prefer? 1 2 CCT = 3501 K D uv = R a (CRI)= 50 R 9 = -80 CCT = 3501 K D uv = R a (CRI)= 75 R 9 = 20

3 Today s Outline Brief overview of CIE CRI Introduction to TM IES Method for Evaluating Light Source Color Rendition (Including Excel Software) Familiar source examples and demonstrations Results from recent experiment

4 Today s Outline Brief overview of CIE CRI Introduction to TM IES Method for Evaluating Light Source Color Rendition (Including Excel Software) Familiar source examples and demonstrations Results from recent experiment

5 CIE CRI (R a ) Test Source Reference Illuminant (approximately) SAME CCT For further reading see CIE , or Houser K, Mossman M, Smet K, Whitehead L Tutorial: Color Rendering and Its Applications in Lighting. LEUKOS.

6 CIE CRI (R a ) Approximation of Color Samples for R a Color Samples for R 9 R 14 TCS 01 TCS 02 TCS 03 TCS 04 TCS 09 TCS 10 TCS 11 TCS 12 TCS 05 TCS 06 TCS 07 TCS 08 TCS 13 TCS 14

7 CIE CRI (R a ) R Y GY G BG BP P RP (Illustration Only) +20 GY +10 G Y V* R -10 BG -20 PB P RP U*

8 CIE Method for Color Rendering Color Fidelity The accurate rendition of color so that they appear as they would under familiar (reference) illuminants CIE CRI (R a )

9 CRI = 95, Original Image Original Image courtesy of Randy Burkett Lighting Design

10 CRI = 80, Desaturated Image Original Image courtesy of Randy Burkett Lighting Design

11 CRI = 80, Saturated Image (Red Enhanced) Original Image courtesy of Randy Burkett Lighting Design

12 Original Baseline Original image courtesy of Randy Burkett Lighting Design

13 CRI = 80 - Hue Shift

14 CRI = 80 + Hue Shift

15 CRI = 80 Saturated

16 CRI = 80 Desaturated

17 Limitations of Considering Only Fidelity Positive Hue Shift Constant CRI Decrease Saturation Perfect Fidelity CRI = 80 CRI = 80 Increase Saturation Negative Hue Shift

18 Limitations of Considering Only Fidelity Positive Hue Shift Decrease Saturation Constant CRI One measure is not enough! Perfect Fidelity CRI = 80 CRI = 80 Increase Saturation Negative Hue Shift

19 CRI (R a ): A measure of average color fidelity. But what about. saturation changes? hue shifts? color discrimination? color preference?

20 One index is not enough. But how many are needed? And what should they be? Attributes of Color Rendition include: Color Fidelity Color Discrimination Color Preference Tend to be related to saturation, which can be quantified with gamut Sidebar for Further Reading: The more than 25 indices of color rendition that appear in the scientific literature tend to cluster into two categories, those based on comparison to a reference illuminant (i.e., to quantify fidelity), and those related to gamut area (i.e., to quantify increase or decrease in saturation).* * Houser KW, Wei M, David A, Krames MR, Shen XS. Review of Measures for Light-Source Color Rendition and Considerations for a Two-Measure System for Characterizing Color Rendition. Optics Express. 2013; 21(8);

21 Today s Outline Brief overview of CIE CRI Introduction to TM IES Method for Evaluating Light Source Color Rendition (Including Excel Software) Familiar source examples and demonstrations Results from recent experiment

22 Two primary motivations for developing the IES Method: 1. The need for an improved measure of color fidelity 2. The need to provide supplementary information about color rendering ability of any given light source

23 CIE CRI (1965/1974) IES TM (2015) CIE 1964 U*V*W* CAM02-UCS (CIECAM02) 8 color samples 99 color samples Medium chroma/lightness Spectral sensitivity varies Munsell samples only Uniform color space coverage Spectral sensitivity neutral Variety of real objects Fidelity Metric Only Fidelity, Gamut, Graphical, Detailed Ref Illuminant Step Function No lower limit for scores Ref Illuminant Continuous (Uses same reference sources, but blended between 4500 K and 5500 K) 0 to 100 scale (fidelity)

24 IES Method for Color Rendition High Level Average Values Fidelity Index (R f ) Gamut Index (R g ) Core Calculation Engine Modern Color Science New Color Samples Graphical Representations Color Vector Graphic Color Distortion Graphic Detailed Values Skin Fidelity (R f,skin ) Fidelity by Hue (R f# ) Chroma Shift by Hue (R c# ) Fidelity by Sample (R f,ces# )

25 IES Method for Color Rendition Color Fidelity Color Gamut Graphics The accurate rendition of color so that they appear as they would under familiar (reference) illuminants Fidelity Index (R f ) (0-100) The average level of saturation relative to familiar (reference) illuminants. Gamut Index (R g ) ~ when R f > 60 Visual description of hue and saturation changes. Color Vector Graphic

26 b' Fidelity Index: R f Average similarity in appearance of test and reference sources Analogous to CIE R a, greater accuracy Scores of 0 to 100 Scale similar to CIE R a, but high scores harder to achieve Equal weight to all directions of shift Should not be expected to correlate with any single object color a' Reference Source Test Source [Flattened to 2D]

27 b' b' Relative Gamut Index: R g a' Reference Source Test Source a' Reference Source Test Source 15

28 b' Relative Gamut Index: R g R g = 100 A t A r R g > 100: Average increase in saturation R g < 100: Average decrease in saturation a' Reference Source Test Source 15

29 Theoretical Example Original Desaturated Red-Enhanced CRI = 95 CRI = 80 CRI = 80 R f = 93 R f = 78 R f = 78 R g = 100 R g = 90 R g = 110 Original Image courtesy of Randy Burkett Lighting Design

30 Theoretical Example Average values can hide important information! Original Desaturated Red-Enhanced CRI = 95 CRI = 80 CRI = 80 This is limitation of CIE R a, and IES R f and R g R f = 93 R f = 78 R f = 78 R g = 100 R g = 90 R g = 110 Image courtesy of Randy Burkett Lighting Design

31 Color Vector Graphic Gamut is not a dimension of perception. It is best interpreted with reference to a complementary graphic Color Vector Graphic Color Distortion Graphic R f = 81 R g = 101 CCT = 2496 K R a = 88 (Source No. 286)

32 b' Color Vector Graphic COLOR VECTOR GRAPHIC CES CHROMATICITY COMPARISON a' Reference Source Test Source 15

33 b' Color Vector Graphic CES CHROMATICITY COMPARISON a' Reference Source Test Source 15

34 b' Color Vector Graphic CES CHROMATICITY COMPARISON Increased Saturation Decreased Saturation Hue Shift a' Reference Source Test Source 15

35 Theoretical Example Original Desaturated Red-Enhanced CRI = 95 CRI = 80 CRI = 80 R f = 93 R f = 78 R f = 78 R g = 100 R g = 90 R g = 110 Original Image courtesy of Randy Burkett Lighting Design

36 Excel TM Calculation Tool

37 Today s Outline Brief overview of CIE CRI Introduction to TM IES Method for Evaluating Light Source Color Rendition (Including Excel Software) Familiar source examples and demonstrations Results from recent experiment

38 CES01 CES04 CES07 CES10 CES13 CES16 CES19 CES22 CES25 CES28 CES31 CES34 CES37 CES40 CES43 CES46 CES49 CES52 CES55 CES58 CES61 CES64 CES67 CES70 CES73 CES76 CES79 CES82 CES85 CES88 CES91 CES94 CES97 Halogen (MR16) TM-30 Library Source No. 80 R f = 99 R g = 99 R f,skin = 99 R f,h1 = 98 R cs,h1 = -1% R a = 99 R 9 = 93 CCT = 2988 K D uv = LER = 180 Fidelity Index by Sample, R f,cesi

39 CES01 CES04 CES07 CES10 CES13 CES16 CES19 CES22 CES25 CES28 CES31 CES34 CES37 CES40 CES43 CES46 CES49 CES52 CES55 CES58 CES61 CES64 CES67 CES70 CES73 CES76 CES79 CES82 CES85 CES88 CES91 CES94 CES97 High Pressure Sodium TM-30 Library Source No. 56 R f = 32 R g = 61 R f,skin = 34 R f,h1 = 5 R cs,h1 = -48% R a = 17 R 9 = -225 CCT = 1971 K D uv = LER = 382 Fidelity Index by Sample, R f,cesi

40 CES01 CES04 CES07 CES10 CES13 CES16 CES19 CES22 CES25 CES28 CES31 CES34 CES37 CES40 CES43 CES46 CES49 CES52 CES55 CES58 CES61 CES64 CES67 CES70 CES73 CES76 CES79 CES82 CES85 CES88 CES91 CES94 CES97 Neodymium Incandescent TM-30 Library Source No. 88 R f = 86 R g = 109 R f,skin = 84 R f,h1 = 78 R cs,h1 = 11% R a = 77 R 9 = 15 CCT = 2756 K D uv = LER = 136 Fidelity Index by Sample, R f,cesi

41 CES01 CES04 CES07 CES10 CES13 CES16 CES19 CES22 CES25 CES28 CES31 CES34 CES37 CES40 CES43 CES46 CES49 CES52 CES55 CES58 CES61 CES64 CES67 CES70 CES73 CES76 CES79 CES82 CES85 CES88 CES91 CES94 CES97 Linear Fluorescent F32T8/835 TM-30 Library Source No. 38 R f = 75 R g = 99 R f,skin = 84 R f,h1 = 74 R cs,h1 = -12% R a = 79 R 9 = -5 CCT = 3563 K D uv = LER = 349 Fidelity Index by Sample, R f,cesi

42 CES01 CES04 CES07 CES10 CES13 CES16 CES19 CES22 CES25 CES28 CES31 CES34 CES37 CES40 CES43 CES46 CES49 CES52 CES55 CES58 CES61 CES64 CES67 CES70 CES73 CES76 CES79 CES82 CES85 CES88 CES91 CES94 CES97 PC White LED TM-30 Library Source No. 184 R f = 81 R g = 94 R f,skin = 86 R f,h1 = 75 R cs,h1 = -13% R a = 81 R 9 = 0 CCT = 3429 K D uv = LER = 332 Fidelity Index by Sample, R f,cesi

43 CES01 CES04 CES07 CES10 CES13 CES16 CES19 CES22 CES25 CES28 CES31 CES34 CES37 CES40 CES43 CES46 CES49 CES52 CES55 CES58 CES61 CES64 CES67 CES70 CES73 CES76 CES79 CES82 CES85 CES88 CES91 CES94 CES97 Hybrid LED (PC+Red) TM-30 Library Source No. 92 R f = 89 R g = 105 R f,skin = 97 R f,h1 = 91 R cs,h1 = -1% R a = 94 R 9 = 89 CCT = 2776 K D uv = LER = 336 Fidelity Index by Sample, R f,cesi

44 CES01 CES04 CES07 CES10 CES13 CES16 CES19 CES22 CES25 CES28 CES31 CES34 CES37 CES40 CES43 CES46 CES49 CES52 CES55 CES58 CES61 CES64 CES67 CES70 CES73 CES76 CES79 CES82 CES85 CES88 CES91 CES94 CES97 RGB LED TM-30 Library Source No. 108 R f = 80 R g = 114 R f,skin = 81 R f,h1 = 70 R cs,h1 = 15% R a = 71 R 9 = -27 CCT = 3906 K D uv = LER = 299 Fidelity Index by Sample, R f,cesi

45 Existing Sources IES TM-30 R g Phosphor LED Color Mixed LED Hybrid LED Standard Halogen Filtered Halogen Triphosphor Fluorescent, 7XX Triphosphor Fluorescent, 8XX Triphosphor Fluorescent, 9XX Metal Halide IES TM-30 R f

46 Demonstration Live demonstration of SPDs realized using the 7-channel ETC D22, illustrating variations in IES R f, R g, and CIE R a and R 9. The below observations can be partially understood by examination of the 8 slides that follow. What to look for? Source 7 Source 1 Very close to reference conditions Despite a CIE R a of 50 (and IES R f of 64), many would not find this source objectionable because of the manner in which it enhances gamut. 1 vs 2 Despite a 25 point difference in CIE R a, the higher CIE R a source is clearly less desirable 2 vs 3 Despite similar CIE R a and R 9, color rendering is very different. The IES R f and R g measures, plus the graphics, provide more appropriate information. 3 vs 4 Both have similar IES R f and R g, but render objects differently. This illustrates the importance of the color vector graphic. 4 vs 5 Same IES R f, but source 5 has an IES R g that is greater than source 4 by 15 points. Note that source 5 appears more desirable than source 4, despite the fact that CIE R a is 11 points lower. Red rendition is very different, even though CIE R 9 is similar for both. 5 vs 6 IES R f is approximately 80 for both, but source 6 has IES R g of 87 (desaturating), versus IES R g of 115 (saturating) for source 5. Note that CIE R a is higher for the desaturating source (which makes object appear less desirable), yielding a result that is different than many would expect.

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55 Today s Outline Brief overview of CIE CRI Introduction to TM IES Method for Evaluating Light Source Color Rendition (Including Excel Software) Familiar source examples and demonstrations Results from recent experiment

56 Human Judgements of Color Rendition Vary with Average Fidelity, Average Gamut, and Gamut Shape Michael Royer, Pacific Northwest National Laboratory Andrea Wilkerson, Pacific Northwest National Laboratory Minchen Wei, Hong Kong Polytechnic University Kevin Houser, Penn State University Robert Davis, Pacific Northwest National Laboratory Funding Royer, Wilkerson, and Davis supported by U.S. Department of Energy Laboratory Directed Research and Development (LDRD) award Houser subcontracted by Pacific Northwest National Laboratory. Wei supported by stipend through Penn State, with later stages supported by Hong Kong Polytechnic.

57 Relate judgements of color quality to TM-30 measures R g Color Vector Graphic analyses and plots courtesy of Tony Esposito, PhD R f Candidate, Penn State University. Based on simulations using 11-channel LED Cube. Goals Hypotheses Methods Results Discussion Conclusions

58 Relate judgements of color quality to TM-30 measures R g Color Vector Graphic analyses and plots courtesy of Tony Esposito, PhD R f Candidate, Penn State University. Based on simulations using 11-channel LED Cube. Goals Hypotheses Methods Results Discussion Conclusions

59 a priori hypotheses 1. As Rf increases, color would be judged as more normal. 2. As Rg increases, color would be judged as more saturated. 3. Higher levels of Rg would be more preferred than lower levels of Rg. 4. Higher levels of red saturation would be preferred. Goals Hypotheses Methods Results Discussion Conclusions

60 Apparatus and Test Space Goals Hypotheses Methods Results Discussion Conclusions

61 Independent Variables: Rf, Rg, and Gamut Shape R g R f Goals Hypotheses Methods Results Discussion Conclusions

62 Independent Variables: Rf, Rg, and Gamut Shape R g R f Goals Hypotheses Methods Results Discussion Conclusions

63 Independent Variables: Rf, Rg, and Gamut Shape R g R f Goals Hypotheses Methods Results Discussion Conclusions

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67 Participants 28 participants (12 male, 16 female) 19 to 65 years of age (mean male = 44, mean female = 38) Ishihara 24 plate test revealed one redgreen deficient male, not excluded. Goals Hypotheses Methods Results Discussion Conclusions

68 Dependent Measures a priori hypotheses 1. As Rf increases, color would be judged as more normal. 2. As Rg increases, color would be judged as more saturated. 3. Higher levels of Rg would be more preferred than lower levels of Rg. 4. Higher levels of red saturation would be preferred. Normal Saturated Like Shifted Dull Dislike Goals Hypotheses Methods Results Discussion Conclusions

69 Procedures Pre-Experimental Preparation Informed Consent Ishihara Color Screening White Lab Coat Experimental Trials 3 practice trials (2 announced) 26 experimental trials (walk and look within room, await cue from experimenter, complete survey, step out, exchange survey forms, repeat). Goals Hypotheses Methods Results Discussion Conclusions

70 Preference varied systematically. Higher levels of Rg were generally preferred to lower levels of Rg. p = Dislike 130 Model r 2 = 0.68 a priori hypotheses IES TM-30 R g Higher levels of Rg would be more preferred than lower levels of Rg. 4. Higher levels of red saturation would be preferred Like IES TM-30 R f p = Goals Hypotheses Methods Results Discussion Conclusions

71 Preference varied systematically. Higher levels red saturation were preferred (These aren t necessarily the most preferred sources possible, just the most preferred sources from this experiment). Goals Hypotheses Methods Results Discussion Conclusions

72 Same fidelity and gamut, but different gamut shape, can lead to significantly different preference. p = Dislike Model r 2 = IES TM-30 R g Like IES TM-30 R f p = Goals Hypotheses Methods Results Discussion Conclusions

73 Same fidelity and gamut, but different gamut shape, can lead to significantly different preference. Goals Hypotheses Methods Results Discussion Conclusions

74 Preference increased with red-saturation, with limits. Mean Preference Rating 8 7 Dislike y = x x x R² = Like 1-30% -20% -10% 0% 10% 20% 30% Hue Bin 16 Chroma Shift (R cs,h16 ) Goals Hypotheses Methods Results Discussion Conclusions

75 Participant Preference Rating Post-hoc modeling of preference 7 6 Less Liked More Liked R² = TM-30 Model Predicted Preference Rating Best Model for Preference: Like-Dislike = (R f ) (R cs,h163 ) (R cs,h16 ) Goals Hypotheses Methods Results Discussion Conclusions

76 What about existing light sources? 50% 40% 30% 20% 10% Experimental Preferred Zone* R cs,h16 0% -10% -20% -30% -40% -50% Goals Hypotheses Methods Results Discussion Conclusions

77 What about existing light sources? IES TM-30 R g Experimental Preferred Zone* Phosphor LED Color Mixed LED Hybrid LED Standard Halogen Filtered Halogen Triphosphor Fluorescent, 7XX Triphosphor Fluorescent, 8XX Triphosphor Fluorescent, 9XX Metal Halide IES TM-30 R f Goals Hypotheses Methods Results Discussion Conclusions

78 Results from this small study When combined in regression models, the TM-30 measures demonstrated excellent correlation with participant evaluations Preference model r 2 = 0.94 Normalness model r 2 = 0.83 (not discussed) Saturation model r 2 = 0.95 (not discussed) Because of gamut shape, visually detectable differences in R f and R g are as little as zero points. Sources that increased saturation in red were liked (These data suggest R CS,H16 of about 2% to 16%) Commercially available sources are unlikely to be optimized for preference (at least partially due to the lack of appropriate optimization tools) Goals Hypotheses Methods Results Discussion Conclusions

79 Acknowledgments The slides in this presentation include images, ideas, and contributions from: Randy Burkett, Randy Burkett Lighting Design Tony Esposito, Penn State University Michael Royer, Pacific Northwest National Laboratory The experiment was performed by: Michael Royer, Pacific Northwest National Laboratory (Principal Investigator and Lead Author) Andrea Wilkerson, Pacific Northwest National Laboratory Minchen Wei, Hong Kong Polytechnic Kevin Houser, Penn State University Robert Davis, Pacific Northwest National Laboratory

80 Kevin W. Houser, PhD, PE, FIES Professor of Architectural Engineering The Pennsylvania State University 104 Engineering Unit A University Park, PA USA Phone: (814) khouser@engr.psu.edu Additional TM Collaborators: Resources Dr. Dale Tiller Dr. Xin Hu Dr. Bill Thornton Dr. Steve Fotios Mr. Mike Royer 80