One of the most recognizable metrics for lighting performance is the color rendering index (CRI), which has been in use in the lighting industry since the 1960s. However, a new metric might just represent a paradigm shift for manufacturers and consumers. The Illuminating Engineering Society’s Technical Memorandum-30 (TM-30) is expected to emerge as a modern metric for modern lighting performance.
For any upcoming lighting changes you might be planning, it is important to keep up and learn more about TM-30.
Color Rendering Index
The Lighting Research Center at Rensselaer Polytechnic Institute describes the CRI as “a measure of a light source’s ability to show object colors ‘realistically’ or ‘naturally’ compared to a familiar reference source, either incandescent light or daylight.”
For picking out the right lighting fixtures in your facility, these qualities are important. But the main problem with the CRI is that its potential as an evaluative tool is limited because it categorizes white light only in terms of warmness or coolness. That is no longer enough to evaluate lighting.
Even the International Commission on Illumination, which developed the CRI, recognizes its limitations now. While it worked effectively for fluorescent lighting, it does not work as well for LED lighting.
The commission identifies two main technical issues with the CRI. The first is the inherent inaccuracy of color appearance evaluation that comes from the 1974 formulas.
“The second is a limitation of the CRI due to the fact that it is simply a color fidelity metric; that is, the CRI values are based on the color appearance of objects compared to their appearance under the defined reference illuminant,” the commission explains. “Color quality characteristics other than color fidelity are also important, and different analysis methods are required to assess them in the context of lighting applications, tasks and user preferences.”
TM-30 includes a measure of color fidelity like the CRI does, but it also includes color gamut, or “the average level of saturation relative to familiar (reference) illuminants,” says ENERGY STAR. Introducing saturation’s effects provides greater dimension to the CRI’s assessment of just color fidelity.
“While it has been useful for many years, there are substantial limitations to considering only color fidelity,” explains the Department of Energy (DOE). “In fact, color fidelity is not correlated with the color rendering that people prefer.”
The only thing keeping TM-30 from overtaking CRI is the industry itself. Once more manufacturers adopt this metric, it will be the main measurement of lighting quality. As researchers refine TM-30, it is expected to be more widely accepted.
“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),” explains the DOE. “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.”
Whether or not TM-30 replaces CRI (or rather, when it does) is unclear. What is also unclear is what changes TM-30 might undergo in the future, as its developers have stated an intention to revise the index as necessary to best measure color rendering. What is clear is that the transition seems to be well underway for the update in color rendering metrics, and understanding TM-30 may be important to identify the best lighting solutions in your facility.
Justin Feit [email protected] is Associate Editor of BUILDINGS.