08 Jul 2008
A recently published standard for testing of solid-state lighting will help to build approval of the technology, but more are needed to complete the picture.
“We are on the cusp of the change to solid-state lighting.”
The Illuminating Engineering Society of North America (IESNA) has recently published a standard, designated LM-79, describing methods for testing the output, energy efficiency and chromaticity of solid-state lighting (SSL) products. Along with a standard from the American National Standards Institute (ANSI) that specifies colour ranges for SSL, designated C78.377-2008, these are two fundamental standards needed for widespread adoption of the technology. More standards are needed, however, before this becomes a reality.
"These are early days for standards around SSL, which is still a nascent technology for lighting," Kevin Dowling of Philips Solid-State Lighting Solutions (formerly Color Kinetics) commented to optics.org. "Even though LEDs have been around for decades, they have only been used for lighting in the last few years, and for general illumination almost not at all. We're really on the cusp of the change."
Dowling participated in the drafting of both of the published standards, which have been described as being the first such standards for SSL in the US. "That's a fair claim, although there are some existing standards that could be considered to be related," he said. "There are standards around lighting from the Society of Automotive Engineers that include LEDs, and the International Commission on Illumination also has pre-existing standards for measurement of light output from LEDs. But for lighting specifically, these two probably are indeed the first standards."
The next standard to appear will be IESNA LM-80, which deals with lumen depreciation testing of LEDs, arrays and modules. "LM-80 addresses how long an LED can be considered to be alive," said Dowling. "Hopefully it will be completed later this summer."
After that, Dowling hopes that standards for colour rendering can be considered. "The existing colour rendering index, or CRI, was developed by a committee over a long period of time and it's an unsatisfactory measurement of the fidelity of the colour of light," he said. "This area needs a significant amount of work in order to be applied to SSL, and needs some subjective input from human beings as well as lab tests."
The drive towards SSL standards involves a number of different regulatory bodies, with the photometry section at the National Institute of Standards and Technology (NIST) led by Yoshi Ohno playing a significant role. Dowling describes it as a group effort being led by the industry as a whole. "Some people say that it's too early for standards to be written, since SSL technology is changing so quickly, but I disagree. I think that some general measurement standards can be put in place without waiting for the technology to completely settle down, which won't happen for some years."
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