For over 80 years, lighting professionals have been using the Color Rendering Index to evaluate the fidelity of artificial light coloring. Though it has been a valuable tool for many years, there are several reasons why it is now outdated and time to move on to the TM-30-15.
- CRI was determined by comparing a reference light source to a product with only eight color samples. This allowed for manufacturers to develop light sources that would score higher while possibly oversaturating certain colors. The resulting CRI would make product comparisons difficult because two products may have the same CRI, but the color saturation may be very different.
- A quick comparison of the spectral power distribution curves of any gas illuminant, like a compact fluorescent lamp (shown below), will illustrate the incomplete nature of their distributions. LEDs on the other hand may test lower under CRI, but display a more even distribution of color. A recent customer of mine has a paint shop where he uses a color wheel to test the accuracy of the light source. He currently has older lights that he wants to change out to be more energy efficient but he can’t compromise on the color quality. The vendor on the project was looking at tri-phosphor (high CRI) T8 lamps but they couldn’t find an option that was efficient enough to qualify for incentives. After trying many lamps the vendor discovered that the lamp needed to be >88 CRI, however, he was surprised to discover that all of the TLED lamps that he tested met the customer’s strict color requirements at a lower CRI. This is because the LED had better color representation over the entire spectral power distribution curve. Notice the more gradual smoother curve for the LED graph on the left below.
Royer, M. (2015). Limitation of Average Values, Retrieved from http://energy.gov/sites/prod/files/2015/09/f26/tm30-intro-webinar_9-15-15.pdf
- The TM-30-15 has three main output measures that offer more ways to evaluate the color quality of a light source. Color fidelity (Rf), Gamut (Rg), and a color vector graph (circle graph below) are the main evaluation metrics for TM30. In addition to the three main measures, there are also other measurements for specialized interests, like the skin color rendering index (Rf,skin) which tell you how accurately skin color will be perceived under a light source..
The new TM30 measure is a great resource to evaluate the performance of a light source by simply looking at a spec sheet. Because of the different measurement outputs, lighting professionals can not only evaluate the color fidelity with more precision, they can also more easily see the color saturation over the entire color spectrum. It’s now time to replace the antiquated CRI measure with the TM30.
For further information please refer to the “Understanding and Applying TM-30-15” presentation at: http://energy.gov/sites/prod/files/2015/09/f26/tm30-intro-webinar_9-15-15.pdf
Royer, M. (2015). F32T8 835 (Source No.37), Retrieved from http://energy.gov/sites/prod/files/2015/09/f26/tm30-intro-webinar_9-15-15.pdf