CRI – Lighting by Jeffrey

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In my last blog post, I explained the recent recommendation by the CIE (International Commission on Illumination) to move away from CRI and replace it with R_f, CIE General Color Fidelity Index. Almost immediately, I was asked why. It’s a good question. On the surface, they appear to be very similar.

Both use a zero to 100 ranking system
Both use the same Spectral Power Distribution (SPD)
Both compare a source against reference colors

This last point is what makes the biggest difference.

Color Rendering Index (CRI) uses only eight reference colors. All eight are pastels with similar levels of saturation. For years, known flaws included the lack of red, bold colors and flesh tones, but because incandescent light does a good job rendering pastels, it never raised much concern. The rise of LED laid bare the failures.

To solve this key flaw, R_f uses 99 reference colors, evenly spread across the color spectrum. These are also colors drawn from real-world objects and dyes. A wider sampling will deliver a more realistic metric.

One additional pushback I have heard concerns the similar results garnered by each test method. Perhaps the CRI is 90 and R_f is 92. Of course, that is possible. MicroSoft Windows 1.0 could allow us to write a letter and the same can be said about today’s most current operating system. The difference is in all of the other features. As we begin to use and understand R_f, the added features will grow in value. With the added data provided by R_f, one might find one light source does a great job rendering wood tones and another a better with bold blue colors. As lighting professionals, we can select the light that best suits the application. As the CIE address the other know flaws, new measurements will build on this foundation to be more robust method of color measurement.

I can’t stress this more. Find a way to introduce yourself to this new metric. Like commercial lighting professionals have realized before us, the advantages will far outweigh the learning curve.

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You may have heard that the CIE (International Commission on Illumination) has finally agreed with numerous illumination and color of light experts to abandon the Color Rendering Index (CRI) method of measuring the quality of white light. That was the easy part (not really, it took a long time, but stick with me.)

While those of us who simply want to specify and use good light have referred to this characterization as CRI, the CIE calls it R_a, CIE General Color Rendering Index. They are recommending a replacement with R_f, CIE General Color Fidelity Index.

When we lived in an incandescent and fluorescent world, CRI worked fine. As we started to employ more fluorescent and then a total LED replacement, the known flaws in the CRI system became more and more apparent. Something different was needed. Early on, the CIE admitted that CRI was not acceptable, but was noncommittal on a replacement. This world organization is known for its detailed deliberation. When it makes a decision, it comes with a lot of weight.

Over the years, a number of replacement concepts were proposed and rejected until the lighting community was presented with TM-30. While there were a few objections, most everyone agreed this was a superior metric. Much of the commercial lighting industry has already begun using TM-30. We decorative lighting folks have maintained an allegiance to CRI for very clear reasons. It was easy. 100 = good; zero = bad. If we’re close to 100, we should be satisfied. Besides, we have just begun to take light quality seriously, some slack was needed to be given to those of use less technically inclined.

One reason TM-30 is so fully supported is because it is actually two different measurements packed into one metric. There is a one-for-one replacement for CRI or R_a. That is R_f (fidelity.) It also measures color saturation and that portion is call R_g (gamut.) The CIE also recognizes that a single fidelity measurement does not tell the whole story. They are setting a foundation for a more comprehensive metric that could be TM-30, or could be something else.

What Can Decorative Lighting Expect?

I understand change is hard. I was around when decorative manufacturers, retailers and the design community needed to digest a new set of data points. Color Temperature and CRI were rarely discussed and poorly understood prior. Nonetheless, we all rose to the occasion. Here’s what we should expect to see in the coming months and years.

Timing	Metric
The past and currently	CRI	We may see many decorative manufacturers cling to the old measurement
Coming Soon	CRI + R_f	To help in the transition, showing both numbers will help users understand the number and the benefits of change
Future	R_f	With the term an integral part of the dialog, CRI can then be eliminated
The Desired Future	R_f + R_g (?) / TM-30 / ?	Everyone understands we need a more comprehensive metric. Will TM-30 be the answer, or a stepping stone to something else?

I don’t know how long it will take for the decorative lighting world to see this change, but I do know, TM-30 was adopted a lot faster than I had expected in the commercial space. For that reason, I urge you to take a minute or two and understand what could be coming your way. Remember when you were the only one who understood CRI? That time is coming again.