What Is ANSI/IES-TM-30?

The ANSI/IES TM-30 Standards are an internationally accepted set of guidelines for characterizing the color rendition (color rendering) performance of virtually any light source, such as LEDs.

Development of TM-30

Multiple methods of characterizing light source color rendition—the CRI, GAI and CQS indices—had been developed previously. However, many experts still found the measurement and characterization of light source color rendition to be insufficient. Thus in 2014, the Color Metrics Task Force of the Illuminating Engineering Society (IES) developed a new method for characterizing light sources. This new system, called TM-30, provides a set of measures for describing color rendering capabilities that match closest to the range of colors humans perceive.

The new standard system was released in 2015 as ANSI/IES TM-30-15; the IES Method for Evaluating Light Source Color Rendition, Technical Memorandum 30-15¹. It established the TM-30 method for measuring light source color rendering capabilities and set out some standard formats for lighting manufacturers to report this information. Subsequent updates and refinements have been released in 2018 as TM-30-18, and in 2020 as TM-30-20. 

Elements of TM-30

The TM-30 provides three approaches to analyzing color rendering:

• R_f, color fidelity, or hue: R_f gauges how similar or dissimilar a color is to the reference. For example, is something deep red or pink? Scores range from 0 to 100, with 100 indicating an exact match. R_f is a calculation that considers both chromaticity and saturation under the test source and reference illuminant, then determining the arithmetic mean of those color differences.
• R_g, gamut, or saturation: R_g describes how much color is there. The R_g scale ranges beyond 100, which indicates oversaturation. Scores below 100 indicate less saturation than the reference. R_g is a measure of the area spanned by the average coordinates of the CES in each hue-angle bin.
• Color vector graphic: TM-30 creates a graphical report that plots color averages for 16 hue bins and Rf and Rg scores for the 99 color samples.

Although TM-30 and CRI both use fidelity as an attribute, you cannot compare or swap TM-30 and CRI scores.

Using TM-30 to Characterize Light Sources

Today, the TM-30 system is an effective method for evaluating color rendering of LED light fixtures. A key differentiator for TM-30 is that it uses 99 color samples (CES) instead of the CRI base of 8 TCS. For a given LED fixture, its TM-30 scores can be reported numerically and represented graphically as a 2- dimensional color vector graphic. The vector graphic shows one circle (black line), representing the reference sample colors, overlaid with a second circle (red line) representing the color rendition of those samples by the test light source. Variance of the red circle from the reference black circle indicates the color fidelity of the light source.

Example of a color vector graphic (sample 111 RGB). The black circle is the reference illuminant; the red circle charts the light source under test to compare to the reference source.

The color vector graphic makes it easy to see at a glance how closely a light source matches the reference illuminant. For ease of use, the TM-30-18 introduced “bins” that categorize the 99 color samples into groups. Each bin is shown as one “slice” of the color vector circle.  

Fidelity and Gamut

In the TM-30 approach, light sources are scored based on two metrics, Fidelity (Rf, analogous to the CRI value) and Gamut (Rg, analogous to the GAI value). However, TM-30 uses the CAM02-UCS (a’, b’) color space rather than the 1931 (x, y) or 1976 (u’, v’) CIE color spaces. The rationale for this change in discussed in the standard.

Although it is sometimes mischaracterized as a two-measure system, TM-30 goes beyond reporting just these two average values. It incorporates additional concepts such as gamut shape (defined as the average pattern of color shifts across different hues) and chroma shift. As a result, “the TM-30 Color Vector Graphic and Local Chroma Shift values capture information about color rendition that's impossible to describe with global average measures but is pertinent to more completely quantifying color rendition and understanding human evaluations of color quality in the built environment.”²

To learn more, refer to the Help Center articles:

FAQ -> Color Quality Metrics

White Papers -> Achieving Optimal Color Rendition with LEDs

REFERENCES

1. IES Method for Evaluating Light Source Color Rendition. Illuminating Engineering Society, Technical Memorandum ANSI/IES TM-30-20. 2020.
2. Brodrick, J., “Fine-Tuning the Characterization of Color Rendition with Chroma Shift and Gamut Shape.” U.S Department of Energy, Office of Energy Efficiency & Renewable Energy, December 20, 2017.

-------------------------------------------------------------------------------------------------------------------

Luminus Website https://www.luminus.com/

Luminus Product Information (datasheets): https://www.luminus.com/products

Luminus Design Support (ray files, calculators, ecosystem items: [power supplies, lenses, heatsinks]): https://www.luminus.com/resources

Luminus Product Information sorted by Applications:  https://www.luminus.com/applications

Where to buy Samples of Luminus LEDs: https://www.luminus.com/contact/wheretobuy.

--------------------------------------------------------------------------------------------------------------------

Technical Support Contact Information: [e-mail]

Sales Support Contact Information: [e-mail]

Customer Service Support Contact Information: [e-mail]