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Is the Color-Rendering Index (CRI) on its Way Out?

Is the Color-Rendering Index (CRI) on its Way Out?

SHEPHERDSTOWN, W.V. —The way in which lighting designers specify the color-rendering properties of white light – and white light’s ability to alter humans’ perception of color – is about to change, thanks to the development of tunable white light and a near-revolutionary new way of specifying its color impacts, as “first-step-detailed” by the Illuminating Engineering Society (IES) in its Technical Memorandum-30 (TM-30). On the way out: The color-rendering index (CRI): Established in 1964, CRI categorizes white light only in terms of its warmness or coolness.

This fascinating topic was the focus of the National Lighting Bureau’s “TM-30 Now” panel discussion held at the Bureau’s 2017 Annual Lighting Forum, moderated by EdisonReport Editor and Publisher Randy Reid. Panelists included IES Industry Relations Manager Mark S. Lien, LC, CLEP, CLMC, HBDP, LEED BD&C; Greg Yeutter, with lighting-manufacturer LUXTECH; and Randy Burkett, FIALD, FIES, president of Randy Burkett Lighting Design, Inc.

The method being proposed in TM-30 uses two metrics to describe a light source’s color-rendering properties: fidelity, which resembles CRI in many respects, and saturation, considered through an all-new metric called “gamut” that indicates how saturated an illuminated color appears to be.

While progress is being made on both metrics, the fidelity metric is closer to finalization than the gamut metric. Nonetheless, as Lien cautioned and other panelists agreed, TM-30 is not a final document: “It will be changed,” Lien emphasized, noting that optimal finalization will result in an American national standard, via the IES, and, hopefully, an international standard, via the Commission Internationale de l’Eclairage (the International Commission on Illumination, or CIE). He warned that, because near-term change is inevitable, fully adopting the “working” metrics in TM-30 would be premature. He commented that the IES developed and issued TM-30 solely as an initial, “test” process, for lighting experts to evaluate and improve.

Right now, the most daunting challenge associated with TM-30 is not so much finalizing the fidelity and gamut metrics as it is helping people understand them and how they interrelate. Even people in the lighting industry need this education.

The panelists noted that, based on research conducted at Pacific Northwest National Laboratory, people prefer saturated colors to “accurate” or higher-fidelity color rendering, a finding reinforced anecdotally by sales of Kodak’s consumer films: Users preferred films that created more saturated colors, making fall leaves look warmer and skies appear as a deeper blue.

Watch and listen to the panel discussion here:

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