The frequently asked questions shown below cover TM-30 development and logistics.

1. What is TM-30?

Knowledge Level: *

IES TM-30-15 is a document approved by the Illuminating Engineering Society (IES) that describes a method for evaluating light source color rendition. The method encompasses several individual measures and graphics that complement one another and provide a comprehensive characterization of how the light will affect the color appearance of objects. The three highest-level components of the system are the Fidelity Index (Rf)Gamut Index (Rg), and Color Vector Graphic.

Numerous sub-indices are also available if more detailed information is necessary. These document things like the color fidelity of reds, the chroma shift of reds, or the fidelity of skin tones. In many cases, these more detailed values are critical to understanding the performance of a source.

2. Who developed TM-30?

Knowledge Level: *

TM-30 was developed by the Illuminating Engineering Society’s (IES) Color Metrics Task Group. The Task Group was comprised of seven voting members with backgrounds in lighting research, manufacturing, or specification. The Task Group worked under the IES Color Committee, which subsequently voted to approve the document, along with the IES Technical Review Council and IES Board of Directors. Majority approval was required at each balloting step. In total, more than 30 people voted on the TM-30 document, with more than 90% approving.

3. Why was TM-30 developed?

Knowledge Level: *

The existing color rendering metric widely used in the lighting industry, the International Commission on Illumination’s (CIE’s) General Color Rendering Index Ra (commonly called CRI), was developed more than 50 years ago, and has been unchanged in the last 40. Although it has served a vital purpose, its limitations are widely recognized, including by the CIE. The CIE has been working on a replacement or alternative for more than 25 years, and many researchers have developed and proposed new metrics. The IES Color Metrics Task Group was charged with evaluating the current literature and formalizing a recommended method, with the goal of providing a near-term solution to the limitations of CRI.

4. Is TM-30 supported by research?

Knowledge Level: **

The developers of TM-30, the IES Color Metrics Task Group, examined and synthesized the research of numerous other groups in developing the method. Among other details, the group examined the uniformity of color spaces [1, 2, 3, 4, 5], the effect of the quantity and type of color samples [1, 6], and the utility of various characterizations of color rendering [7, 8, 9]. This extensive review provides a solid theoretical foundation for the TM-30 method.

Now that TM-30 has been published, ongoing research is focusing on the meaning and utility of the values. Although much can be learned from existing research, the scope of the measures included in TM-30 is greater than other measures; that is, it goes beyond average fidelity and average gamut measures. Several studies have shown that these additional measures for describing color rendering, such as those documented in TM-30, can improve the correlation between quantifications and human judgments [10, 11, 12].

  1. Smet KAG, David A, Whitehead L. 2015. Why color space uniformity and sample set spectral uniformity are essential for color rendering measures. Leukos 12(1–2):39–50.
  2. Luo MR, Cui G, Li C. 2006. Uniform colour spaces based on CIECAM02 color appearance model. Color Research and Application 31(4): 320–330.
  3. Sándor N, Schanda J. 2006. Visual colour rendering based on colour difference evaluations. Lighting Res Technol 38(3):225–239. DOI: 10.1191/1365782806lrt168oa.
  4. Luo MR, Gu HT, Liu XY, Liu HY, Wang BY. 2015. Testing colour rendering indices using visual data under different LED sources. Proceedings of the 28th CIE Session. Manchester, UK. CIE Publication 216:2015 1(1).
  5. Jost-Boissard S, Avouac P, Fontoynont M. 2015. Assessing the colour quality of LED sources: Naturalness, attractiveness, colourfulness and colour difference. Lighting Res Technol 47:769–794. DOI: 10.1177/1477153514555882.
  6. David A. 2014. Color Fidelity of Light Sources Evaluated over Large Sets of Reflectance Samples. Leukos 10(2):59–75, DOI: 10.1080/15502724.2013.844654.
  7. Houser K, Wei M, David A, Krames M, Shen X. 2013. Review of measures for light-source color rendition and considerations for a two-measure system for characterizing color rendition. Opt Expr 21(8):10393.
  8. Smet KAG, Ryckaert WR, Pointer MR, Deconinck G, Hanselaer P. 2011. Correlation between color quality metric prediction and visual appreciation of light sources. Opt Express 19(9):8151–8166.
  9. Rea MS. 2010. A practical and predictive two-metric system for characterizing the color rendering properties of light sources used for architectural applications. Proceedings of SPIE vol 7652. 765206-1-7.
  10. Wei M, Houser KW, David A, Krames MR. 2016. Effect of Gamut Shape on Color Preference. CIE 2016 “Lighting Quality & Energy Efficiency”, Melbourne, Australia, 2016.
  11. Wei M, Houser KW. 2016b. Color preference under light stimuli characterized by a two-measure system: a pilot study. IES Research Symposium III – Light + Color. Gaithersburg (Maryland), USA.
  12. Royer MP, Wilkerson AM, Wei M, Houser KW, Davis R. Human Judgements of Color Rendition Vary with Average Fidelity, Average Gamut, and Gamut Shape. Submitted for Publication.

5. Will TM-30 be revised?

Knowledge Level: *

Like all technical documents, TM-30 may be revised in the future. However, it is currently a final document that may be used in design and engineering processes.

6. Is TM-30 approved by the CIE?

Knowledge Level: *

TM-30 was developed by the Illuminating Engineering Society. IES documents are analogous to CIE (International Commission on Illumination) documents, and either can be adopted as national or international standards by groups such as ANSI (American National Standards Institute) or ISO (International Standards Organization). The CIE has been working to develop new color rendering measures for many years, but has not yet adopted any new measures. A recent CIE position statement has indicated that components of TM-30 are in working drafts for new CIE documents.

7. Will TM-30 replace CRI?

Knowledge Level: *

TM-30 includes a measure of color fidelity that is analogous to the CIE general color rendering index Ra, which is commonly referred to as CRI. It is possible that TM-30’s Rf will supplant Ra, if it achieves widespread use in the industry. However, CRI was developed by the CIE, whereas Rf was developed by the IES. The CIE is currently developing new color rendering measures, which may or may not replace CRI.

8. How is TM-30 different from CIE CRI?

Knowledge Level: *

TM-30 is a method for evaluating light source color rendition. It includes numerous measures that quantify different aspects of color rendering, such as fidelity and gamut. In contrast, CIE CRI is purely a method for evaluating color fidelity. While it has been useful for many years, there are substantial limitations to considering only color fidelity. In fact, color fidelity is not correlated with the color rendering that people prefer [e.g., 1,2]. TM-30 does include a fidelity measure, although it is different from CRI in several key ways (see question 9).

  1. Smet KAG, Ryckaert WR, Pointer MR, Deconinck G, Hanselaer P. 2011. Correlation between color quality metric prediction and visual appreciation of light sources. Opt Express 19(9):8151–8166.
  2. Royer MP, Wilkerson AM, Wei M, Houser KW, Davis RG. Human Judgments of Color Rendition Vary with Average Fidelity, Average Gamut, and Gamut Shape. Submitted for Publication.

9. How is TM-30 Rf different from CIE CRI (Ra)?

knowledge Level: **

CRI is the common name for the CIE’s general color rendering index Ra. Like CRI, TM-30 Rf is a measure of average color fidelity; however, TM-30 Rf addresses many of the scientific shortcomings of the older metric, which was first adopted in 1965. Two of the main differences are the color space in which the colors are evaluated (CIE U*V*W* versus CAM02-UCS), and the number and type of samples considered (8 versus 99). Whereas Rf was formulated to have approximately the same scale as CRI, there is usually a difference in scores for individual sources, due to the underlying spectral differences. In particular, sources with narrow spectral features that were optimized for the samples used in CRI typically have lower Rf scores than CRI scores. Similarly, CRI is systematically biased against sources that increase red chroma, which can be particularly detrimental when attempting to identify preferred sources; this is primarily due to the color space used for CRI.

The color space, chromatic adaptation transformation, quantity of color spaces, and type of color samples all contribute to differences in score for Rf and CRI [1, 2]. Each contributes anywhere from minimal to more than 8 points difference in score for any given source.

  1. Smet KAG, David A, Whitehead L. 2015. Why color space uniformity and sample set spectral uniformity are essential for color rendering measures. Leukos 12(1–2):39–50.
  2. David A, Fini P, Houser K, Ohno Y, Royer M, Smet K, Wei M, Whitehead L. 2015. Development of the IES method for evaluating the color rendition of light sources. Opt Expr 23(12):15888.

10. How is TM-30 different from CQS?

Knowledge Level: **

The color quality scale (CQS) was one of several past proposed metrics that led to the development of TM-30. Like CQS, TM-30 includes multiple average measures and graphical representations. However, TM-30 uses further-improved color science, a more comprehensive set of color samples, and does not include an absolute measure of color preference.

11. When can I start using TM-30?

Knowledge Level: *

TM-30 is an approved document and can be used immediately.

12. When will TM-30 be an industry-wide standard?

Knowledge Level: *

TM-30, like CRI, is a technical report. After it achieved widespread use, CRI was written into required standards from ANSI (American National Standards Institute) and ISO (International Standards Organization). TM-30 has the potential to achieve the same status, but it must reach an appropriate level of use within the industry. The timeline for this is undefined. Importantly, just because TM-30 is not a required standard does not mean it cannot be used to improve the engineering and specification of light sources.