Why TM-30 Might Be a Better Metric for Your Next Lighting Plan Than CRI

For decades, lighting showroom professionals have relied on the Color Rendering Index (CRI) as a guideline when designing a lighting plan or selecting fixtures for clients. At the ALA Conference in Palm Beach in September, a packed room of ALA member manufacturers, showrooms, and reps learned why the relatively new TM-30 standard makes better sense in the age of LED.

“This might be a little controversial, but I believe that color rendering is more important than color temperature,” stated featured speaker Jason Livingston, LC, principal of Studio T+L, and author of the textbook Designing with Light: The Art, Science, and Practice of Architectural Lighting Design.

As co-chair of the Illuminating Engineering Society (IES) Color Committee, Livingston is well-versed on the topic.  “I know that one of the first things many of us think about when we think about color rendering is CCT, but we need to understand that our visual system adapts [to our environment]. When you first walk into a room, you ‘see’ that it is of a given color temperature – which will make some sort of an impression on you, whether positively or negatively – but within just a few minutes, your visual system has normalized that CCT to just plain white, and it stops having the kind of impact that it did initially.”

The CRI metric has worked well for years when the lighting world primarily consisted of incandescent. As lighting technology has evolved to include fluorescent and now LED, the CRI metric is revealing some flaws. 

When fluorescent light sources appeared in the 1940s, there was noticeable color shift (i.e. less vibrancy). It wasn’t until 1965 that the CIE (International Commission on Illumination) introduced CIE-13, which was its method for measuring color rendering. 

“I want you to consider that we’re talking about a technology – CRI – that’s from 1965, and that was last updated in 1995. In computer terms, it’s like a Windows DOS machine that is now running Windows XP,” he joked, adding, “There have been efforts to improve CRI, but none of them have succeeded.” 

There have also been advances in the mathematical models of human vision since 1965, he explained, but these new models have not been incorporated into the CRI calculation because the decision needs a unanimous vote from members of the CIE, which it has been unable to achieve.

Livingstone noted that, over time and with the advancement of the highly diverse spectra of LEDs, discrepancies became apparent in the color appearance of objects compared to the CRI value.  “This became a big topic of concern at the IES as it became clear that LEDs were going to become a dominant light source and that the color rendering metric we had was not up to the task of giving us specific information,” he said.  

The IES’ Color Committee began developing a new system for measuring color rendering. The result – ANSI/IES TM-30-24 – is a national standard that published by the Illuminating Engineering Society in 2015, updated in 2018, and will have a new update shortly. 

Livingston performed a much deeper dive into the capabilities of TM-30 versus the limitations of CRI. (For example, CRI measures only 8 color samples, while TM-30 uses 99 color samples in its calculations.)

ALA showroom members at Conference were especially interested in learning more about the advantages of the TM-30 metric and how it can lead to a better color rendering result because it incorporates color preference, vividness, and fidelity into its calculations. 

One challenge facing widespread adoption of TM-30 is the need for manufacturers to jump on board with providing TM-30 metrics just like they have with CRI. “Many manufacturers are probably going to give the information that comes from the LED manufacturer,” Livingston stated. On a positive note, he mentioned that there are at least four manufacturers that have a spectroradiometer with a TM-30 calculator. 

Since color rendering is not a standard where compliance is mandatory like it is with safety issues, change will happen slowly. And unlike safety concerns, TM-30 testing would be done at the manufacturer level and not by an independent lab. 

While widespread adoption of TM-30 is not going to happen immediately, it is important for all ALA members to understand that it will be impacting their business soon. Manufacturers need to be aware that this metric is going to be increasingly requested by lighting designers and should explore how to accommodate them. Providing the most up-to-date specification information to lighting showrooms and designers will ensure a manufacturer’s brand becomes preferred by lighting professionals.  Offering TM-30 specs will also serve as a differentiator between manufacturers who offer more precise color rendering and those who do not.

ALA members can stay abreast of the latest innovations in lighting technology by listening to one of ALA’s educational sessions (either live or recorded) and by attending the annual Conference. Next year’s Conference will be held Sept. 7-9, 2025, in Louisville, Ky. 
  

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https://www.energy.gov/eere/ssl/tm-30-frequently-asked-questions