IES: New Method for Evaluating Light Source Color Rendition

Illuminating Engineering Society

The Illuminating Engineering Society of North America (IES) has announced the publication of IES Method for Evaluating Light Source Color Rendition (TM-30-15), the most recent addition to the Technical Memorandum Series (TM).

Quantifying the color rendition characteristics of a light source is a complex problem. Many aspects of color rendition – such as color fidelity and color discrimination – should be simultaneously considered during the design and specification process. There is no one metric or measure that can accurately quantify all aspects of color rendition and/or identify the most desirable light source for every application.

This Technical Memorandum describes a method for evaluating light source color rendition that takes an objective and statistical approach, quantifying the fidelity (closeness to a reference) through a Fidelity Index (Rf) and gamut (increase or decrease in chroma) through a Gamut Index (Rg) of a light source. The method also generates a color vector graphic that indicates average hue and chroma shifts, which helps with interpreting the values of Rf and Rg.

TM-30-15 provides equations and direction for calculating Rf and Rg, including the spectral reflectance functions for 99 Color Evaluation Samples (CES). A software tool is included with TM-30-15 to aid in calculation and display of the results. The TM-30-15 color rendition 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.

To facilitate understanding of the new color metric, the IES and the U.S. Department of Energy are co-sponsoring two free Webinars. The first of these,Understanding and Applying TM-30-15 is scheduled for September 15 from 1:00p.m. to 2:30p.m. EDT. The Webinar will cover the basics of the new method, while also discussing the development process and the ongoing steps toward widespread adoption. Leading the presentation are Michael Royer (Pacific Northwest National Laboratory) and Kevin Houser (Penn State University). Both Royer and Houser are members of the IES Color Metric Task Group, which was primarily responsible for the development of TM-30-15.

The second Webinar, A Technical Discussion of TM-30-15 is scheduled for September 22 from 1:00p.m. to 2:30p.m. EDT. The Webinar will focus on the underlying math and color science that make up the calculation engine, as well as the details of how the hierarchy of measures is calculated. This Webinar will be conducted by Michael Royer (Pacific Northwest National Laboratory), Aurelien David (Soraa), and Lorne Whitehead (University of British Columbia). Whitehead is also a member of the IES Color Committee.

The IES will offer additional learning opportunities for TM-30-15 at its Annual Conference November 8 – 10 in Indianapolis. A panel discussion entitledDevelopment and Application of the IES Method for Evaluating Light Source Color Rendition will be available to Conference attendees. Panelists will include Randy Burkett (Randy Burkett Lighting Design), Aurelien David (Soraa), Kevin Houser (Penn State University), and Michael Royer (Pacific Northwest National Laboratory). IES Annual Conference registration is available at

“The IES is making a step forward in better defining color rendition to overcome some of the shortcomings of CRI in this age of LED lighting, where we have an unlimited ability to manipulate color spectra. It is our hope that the lighting industry will use the method in TM-30-15 and provide us with feedback so that the TM might eventually lead us to a better color rendering metric,” says Mark Roush, President of the IES.

IES Method for Evaluating Light Source Color Rendition (TM-30-15) is available in print or as a PDF download from the IES at List price: $50.00; IES Member Price: $35.00. ISBN: 978-0-87995-312-6. Softcover, 8 ½ X 11 format, 26 pages + calculation spreadsheets.

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