Color and Lighting: A Rainbow of Options
October 1, 2018
There is a new and better way to gauge just how well a light source accurately illuminates various objects—it literally provides a rainbow of options to show color.
The Old Way: Color Rendering Index
For more than 50 years, we have relied on a Color Rendering Index (CRI) to measure the ability of a light source to faithfully show the colors of various objects as compared with an “ideal” light source, which is usually considered to be daylight.
The CRI has been pretty basic in that it uses only eight color samples to compare the fidelity of the colors rendered by a test light source as compared to one of the samples. You would run the CRI test and get a rating up to 100.
Results were helpful in that you could see the impact different light sources had. Consider a car dealership: in a parking lot full of many different colored cars, some colors look good and others bad, depending upon what light source was being used. Some lights would be good for featuring warm colors, other cold.
Even through CRI was a rather limited metric, manufacturers had gotten used to using it. They focused their development so products maximized performance for those eight color bands, even though a million other colors might not look as good.
It forced many odd conversations when LEDs first came along, because some fluorescent products would have higher CRI ratings than the LEDs. In retail settings this was great cause for concern, pitting merchandisers who didn’t want to sacrifice how their products looked on shelves against those in their organizations who championed the use of LEDs to significantly reduce energy costs.
The quick fix to this dilemma was to add more colors, going from a scale of 8 to 15. There was some initial push back from fluorescent lighting manufacturers, who didn’t want the good thing they had going to come to an end. But as more and more people made the jump to LEDs, these manufacturers also experienced the shift in demand for LED product and the need for appropriate ratings for LED products was theirs as well.
The New Way: TM-30-15
With most CRI testing being done by computer, the next question became, “Why limit it to 15?” In 2015 the Illuminating Engineering Society (IES) published a new Technical Memorandum, "IES Method for Evaluating Light Source Color Rendition."
In addition to expanding the measurement of color fidelity by expanding from 15 to 99 colors, TM-30-15 also includes a gamut index, which measures saturation or how well specific colors are expressed in the light.
The method also provides a color vector graphic, a graphical representation of hue and saturation relative to a reference source. These spider charts clearly point out the good and the bad: if a particular lighting product is saturating greens and blue, but desaturating oranges and reds, you’ll know it.
While TM-30-15 is not an official standard yet, it is going through approval processes and can be adopted as national or international standards by groups such as ANSI (American National Standards Institute) or ISO (International Standards Organization). It’s also gaining traction in the commercial lighting industry with the Design Lights Consortium (DLC) starting to include it as a column on their spreadsheet in 2017.
CRI is important to a number of industries including:
- Health care facilities where the ability to see distinct color differences is important to treating patients
- Manufacturing settings where objects on assembly lines must look a certain way
- Retail environments where products need to be shown in their best light
At EMC, we work with clients in all of these industries to find the right products for their desired CRI. Our best-in-class approach gives us a wide variety of product to choose from. We can also test lighting products in our customers’ facilities so that merchandisers and sustainability managers are both eager to implement their company’s lighting projects.
Tony Johnson is Energy Management Collaborative’s Customer Solutions Specialist. In this role he combines his background in lighting + controls design and solid state light fixture design with his expertise in energy savings to evaluate emerging technologies and solutions for EMC customers. He holds a Bachelor’s degree in architectural engineering from The University of Kansas.