IESNA TM-30-2015 IES Method for Evaluating Light Source Color Rendition.pdf

1、IES TM-30-15IES Method for Evaluating Light Source Color RenditionIES TM-30-15IES Method for Evaluating Light Source Color RenditionPublication of this Technical Memorandum has been approved by the IES. Suggestions for revisions should be directed to the IES.IES TM-30-15Copyright 2015 by the Illumin

2、ating Engineering Society of North America.Approved by the IES Board of Directors, May 18, 2015, as a Transaction of the Illuminating Engineering Society of North America.All rights reserved. No part of this publication may be reproduced in any form, in any electronic retrieval system or otherwise,

3、without prior written permission of the IES.Published by the Illuminating Engineering Society of North America, 120 Wall Street, New York, New York 10005.IES Standards and Guides are developed through committee consensus and produced by the IES Office in New York. Careful attention is given to style

4、 and accuracy. If any errors are noted in this document, please forward them to Director of Technology, at the above address for verification and correction. The IES welcomes and urges feedback and comments. ISBN # 978-0-87995-312-6Printed in the United States of America.DISCLAIMERIES publications a

5、re developed through the consensus standards development process approved by the American National Standards Institute. This process brings together volunteers representing varied viewpoints and interests to achieve consensus on lighting recommendations. While the IES administers the process and est

6、ablishes policies and procedures to promote fairness in the development of consensus, it makes no guaranty or warranty as to the accuracy or completeness of any information published herein. The IES disclaims liability for any injury to persons or property or other damages of any nature whatsoever,

7、whether special, indirect, consequential or compensatory, directly or indirectly resulting from the publication, use of, or reliance on this document.In issuing and making this document available, the IES is not undertaking to render professional or other services for or on behalf of any person or e

8、ntity. Nor is the IES undertaking to perform any duty owed by any person or entity to someone else. Anyone using this document should rely on his or her own independent judgment or, as appropriate, seek the advice of a competent professional in determining the exercise of reasonable care in any give

9、n circumstances.The IES has no power, nor does it undertake, to police or enforce compliance with the contents of this document. Nor does the IES list, certify, test or inspect products, designs, or installations for compliance with this document. Any certification or statement of compliance with th

10、e requirements of this document shall not be attributable to the IES and is solely the responsibility of the certifier or maker of the statement.IES TM-30-15Prepared by the Color Metric Task Group of the IESColor Metric Task GroupM. Royer, ChairIES Color CommitteeW. Luedtke, ChairA. DavidR. BurkettP

11、. FiniK. HouserY. OhnoK. TeunissenM. Wei*C. CowanW. DavisF. FlorentineT. HensleyC. HuntJ. LivingstonN. Miller*M. RoyerM. Thompson*L. WhiteheadM. Wood* Advisory MemberSpecial thanks to K. Smet and L. Whitehead, specifically with regard to the process of establishing the color evaluation samples.IES T

12、M-30-15IES TM-30-15Please refer to the IES Bookstore after you purchase this IES Standard, for possible Errata, Addenda, and Clarifications, www.ies.org/bookstore To download the Excel calculation tool files, please use this URL: http:/www.ies.org/redirect/tm-30/Contents1.0 Introduction.12.0 Scope .

13、23.0 Definitions, Variables, and Procedure23.1 Colorimetric Observer23.2 Test Source 23.3 Reference Illuminant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.4 Color Evaluation Samples (CES) .33.5 Range and Interpolation of Da

14、ta43.6 Calculation of Tristimulus Values.43.7 Color Space and Chromatic Adaptation Transformation 53.7.1 Calculation of Color Coordinates .63.8 Color Difference Formula .73.9 Fidelity Index (Rf) 73.10 Gamut Index (Rg) 83.11 Two-axis System 93.12 Fidelity Measures For Specific Hues Angle Bins And Col

15、or Samples .103.13 Flow Chart 114.0 Limitations and Notes .114.1 Average Values 114.2 Comparison Across CCTs114.3 Energy Efficiency.114.4 Color Samples .114.5 Preferred Chromaticity 134.6 Fluorescence and Whiteness .134.7 Color Rendition Preference.13References.13Annex A - Spectral Reflectance Facto

16、rs .15Annex B - Color Evaluation Samples26IES TM-30-151IES TM-30-15IES Method for Evaluating Light Source Color Rendition1.0 INTRODUCTIONAccurately quantifying the color rendition character-istics of a light source is a complex problem. Many aspects of color rendition, such as color fidelity, color

17、discrimination, or color preference, should be simul-taneously considered during the design and specifi-cation process. There is no one metric or measure that can accurately quantify all aspects of color ren-dition and/or identify the most desirable light source for every application. However, a pre

18、cise and robust method for characterizing color rendition is critical to specifying appropriate light sources and optimizing spectral characteristics of light sources.This Technical Memorandum describes a method for evaluating light source color rendition that takes an objective and statistical appr

19、oach, quantifying the fidelity (closeness to a reference) and gamut (increase or decrease in chroma) of a light source. Importantly, it does not attempt to evaluate human color preference or provide a single number that captures the combined color rendition qualities. However, using the two-dimensio

20、nal characteriza-tion provided by the Fidelity Index (Rf) and Gamut Index (Rg), a user is expected to be able to rely on experience and/or design guidelines to determine what is most appropriate for the specific application in consideration.1,2The method also generates a color vector graphic that in

21、dicates average hue and chroma shifts, and which helps with interpreting the values of Rfand Rg.IES TM-30-15 Method for Evaluating Light Source Color Rendition is based on comparisons of colors as rendered by a given test source and a reference illuminant at the same correlated color temperature (CC

22、T), with the reference illuminant being Planckian radiation up to and including 4500 K, a proportional blend of Planckian radiation and a CIE D Series Illuminant between 4501 K and 5499 K, or a CIE D Series Illuminant at or above 5500 K. This familiar reference-based approach is compatible with a ty

23、pi-cal lighting design process, where color temperature is decided before color rendition is considered. This method utilizes 99 color evaluation samples (CES)each represented by a spectral reflectance factor functionto quantify the difference in color rendition between the test source and reference

24、 illuminant. These samples were statistically down-selected from an initial collection of more than 100,000 measured objects, which were considered to be representative of the world of possible colors.3All of the included color samples are real objects from the database, and the set includes natural

25、 objects, paints, fabrics, plastics, and skin tones. This new set of purposefully selected color sam-ples, as well the use of the most recent and most uniform color space (CAM02-UCS), are two key features that, combined, distinguish this method from others.This Technical Memorandum provides equation

26、s and direction for calculating Rfand Rg, including the spectral reflectance functions for the 99 CES. It is accompanied by a software tool (avalable at http:/www.ies.org/redirect/tm-30/) to aid in calcula-tion and display of the results. It does not establish performance thresholds, nor does it pro

27、vide guid-ance on how to do so. The IES TM-30-15 color rendi-tion method consolidates and synthesizes numerous research efforts that have been ongoing for several years, and was developed by representatives of the manufacturing, specification, and research segments of the lighting industry. Addition

28、al detail regarding the development of the metrics and their benefits is available in “Development of the IES method for evaluating the color rendition of light sources”.3The familiar Color Rendering Index (CRI)4is a color fidelity metric that is in widespread use throughout the lighting industry.*

29、The IES TM-30-15 fidelity measure (Rf) accounts for many of the limitations of CRI that have been well documented.3,5,6,7,8While CRI Raand Rfhave similar scales, they should not be directly compared and performance thresholds for one should not be applied to the other. The relationship is explored f

30、urther in “Development of the IES method for evaluating the color rendition of light sources”.3Rfwas developed specifically to be part of the broad-er IES TM-30-15 measurement system. Importantly, Rfand Rgshare a common set of color samples and uniform color space; thus, the tradeoff between fidel-i

31、ty and gamut can be explicitly demonstrated, and more knowledgeable design decisions that account for multiple aspects of color rendition can be made, compared to using other existing metrics.7*The CIE method for evaluating color rendering is widely referred to as the Color Rendering Index, abbrevia

32、ted CRI. The CIE method employs 14 test color samples and each test color has its own CIE Special Color Rendering Index (note the use of the word Special). Each index is abbreviated as Riwhere i is an integer from 1 to 14. The first 8 values of Riare averaged to compute the CIE General Color Renderi

33、ng Index (note the word General), which is abbreviated a Ra. One way to remember this is 2IES TM-30-15that the subscript i denotes a selected integer and a denotes average. The abbreviations Raand CRI area frequently used interchangeably, and context is usually enough to infer intent, but to be stri

34、ct they are not the same. Any value of Riis also a CRI.72.0 SCOPEThis evaluation method is applicable to light sourc-es and lighting systems intended for general illumi-nation of indoor spaces and some outdoor settings, at light levels where photopic vision is dominant. It is best suited to characte

35、rize nominally white light sources (i.e., those that fall on or near the Planckian locus).3.0 DEFINITIONS, VARIABLES, AND PROCEDURE3.1 Colorimetric ObserverTristimulus values for the color evaluation samples are determined using the CIE 1964 10 standard colorimetric observer, with color matching fun

36、ctions (CMFs) .9,10The 1 nm table is available in “Colorimetry Part 1: CIE Standard Colorimetric Observers”.10The exception is when determining the CCT of the test source, which by definition requires the use of the CIE 1931 2 standard colorimetric observer.9,11,12Also note that, for light source sp

37、ecifications, the CIE 1931 standard colorimetric observer (CMFs, is used to calculate chromaticity coordinates (x, y) and (u, v). The 1964 10 CMFs are used for light sources in this document only for the purpose of calculating color rendition indices. 3.2 Test SourceThe relative spectral power distr

38、ibution (SPD) of the light source in question (test source) is denoted St(). The necessary wavelength range is described in Section 3.5. The tristimulus values of the test source are calculated as follows: (3.2.1)(3.2.2)(3.2.3)where:(3.2.4)As shown, during the calculation process, normaliza-tion occ

39、urs so that tristimulus value Y = 100. This pro-cedure is also followed for the reference illuminant. 3.3 Reference IlluminantThe IES TM-30-15 method compares each test source to a reference illuminant (with SPD denoted as Sr() of the same CCTagain, CCT is calculated using the CIE 1931 2 CMFs. The r

40、eference illumi-nant shall be Planckian radiation, a CIE Daylight (D) Series illuminant, or a combination of the two, depend-ing on the CCT of the test source (Tt). Calculation of both Planckian radiation and the D Series illuminants are covered in “Colorimetry, 3rd ed.”9For calculating the CCT of t

41、he test source (Tt), the method described in “Practical Use and Calculation of CCT and Duv”12may be used. The necessary wavelength range for the reference illuminant is described in Section 3.5.If Tt 4500 K, then the reference illuminant shall be Planckian radiation, which can be calculated as follo

42、ws:(3.3.1)where:(3.3.2)If Tt 5500 K, then the reference illuminant shall be a phase of the CIE Daylight illuminant, which can be calculated as follows:(3.3.3)where , and are functions of wavelength and given in Table T.2 of “Colorimetry, 3rd ed.”9and where:(3.3.4)(3.3.5)where if Tt= Tr 7000 K:(3.3.6

43、)3IES TM-30-15or if Tt= Tr 7000 K:(3.3.7)and where:(3.3.8)If 4500 K Tt 5500 K, then the reference illuminant shall be a proportional mix (denoted with the sub-script M) of Planckian radiation and the CIE Daylight illuminant according to the following equation: (3.3.9)Therefore, the reference illumin

44、ant is given depending on the CCT, Tt, as: (3.3.10)(3.3.11)(3.3.12)The reference illuminants are similar to those used in the calculation of CIE CIE 13.3-19954but instead of a discontinuity at 5000 K, there is a range where the Planckian radiation and CIE Daylight illuminant are blended together. Th

45、e range of 4500 K to 5500 K avoids discontinuity, which may be troublesome when reporting data for color-tunable light sources, and prevents any manipulation of the results (i.e., specifying a source at 4999 K instead of 5000 K, or vice versa). Note that the blended sources shall be normalized so th

46、at each has an equal luminous reflectance factor (Y ).Once the reference illuminant has been calculated, the SPD shall be scaled so that the tristimulus value Y = 100. The tristimulus values can be calculated as: (3.3.13)(3.3.14)(3.3.15)where:(3.3.16)3.4 Color Evaluation Samples (CES)For this method

47、, the color rendition of a test source and reference illuminant are compared using a set of 99 color evaluation samples (CES), the chromaticity of which can be computed under both conditions. The CES were mathematically down-selected from a set of approximately 105,000 spectral reflectance factors,*

48、 which were held by the authors to repre-sent the range of all possible colors of real objects. The complete selection procedure is described in “Development of the IES Method for Evaluating the Color Rendition of Light Sources.”3The mathematical down-selection procedure occurred as follows: First,

49、the samples under consideration were restricted to the volume encompassed by the gamut of the Natural Color System (NCS). This gamut boundary was selected because it approximates the limits for which color error formulas have been tested, and precludes selection of samples from regions with few samples. In addition, the reduced color gamut was considered to better represent typical objects found in most interior rooms than the full gamut the original 105,000 samples. The reduced-gamut set included approximately 65,000 spectral reflectance factors. Next, a set of approximat