ASSIST alliance develops new metric for color properties in retail lighting

June 17, 2010
RPI's Lighting Research Center publishes a new volume in the ASSIST Recommends Series that defines a two-metric approach for specifying light sources to illuminate, and provide good color rendering of retail goods.

Recognizing the shortcomings of CCT (correlated color temperature) and CRI (Color Rendering Index) specifications with emerging light sources such as LEDs, the Alliance for Solid-State Illumination Systems and Technologies (ASSIST) has studied retail lighting. Working under the direction of ASSIST, The Lighting Research Center (LRC) at Rensselaer Polytechnic Institute (RPI) has developed a new metric that augments CRI and aids in specifying optimal light sources to illuminate and render color in retail goods.

The new ASSIST volume includes two issues entitled " Guide to light and color in retail merchandising" and " Recommendations for specifying color properties of light sources for retail merchandising" The first provides a background on CCT and CRI including the advantages a drawbacks of each and how they can be augmented for retail applications. The second recommends a new two-metric approach for specifying light sources.

To achieve good color rendering, ASSIST recommends using CRI along with a new metric called GAI (gamut area index). GAI targets the relative separation of the colors in an illuminated object. A higher GAI equates to greater saturation or vividness of object colors.

Mark Rea, director of the LRC, said, “Broadly speaking, CRI is a measure of how ‘natural’ an object appears, and GAI is a measure of how ‘vivid’ the colors appear. LRC experiments show that light sources which balance both CRI and GAI are generally preferred over ones that have only high CRI or only high GAI.”

The two recently published issues include step-by-step methods to the two-metric approach with the goal of achieving consistent lighting results. Rea said, "The rationale and new methods provided in this ASSIST volume should lead to light source specification that most closely represents a designer’s intentions."

Coincidentally, the LRC story follows another recent attempt at defining new color metrics. Just a few days ago, the NIST (National Institute of Standards and Technology) went public with its new CQS (Color Quality Scale) metric that NIST is proposing as a standard to the international CIE (Commission on Illumination).

ASSIST is a collaboration of manufacturers, research institutions and organizations that is focused on indentifying and overcoming urdles facing solid-state lighting (SSL). ASSIST sponsors include Acuity Brands Lighting, Bridgelux, the China Solid State Lighting Alliance, Cree, Everlight Electronics, the Federal Aviation Administration, GE Lumination, the Industrial Technology Research Institute, LG Innotek, Lighting Science Group, Lite-On, NeoPac Lighting, the New York State Energy Research and Development Authority (NYSERDA), OSRAM, Permlight, Philips, Sharp Laboratories of America, Seoul Semiconductor, the United States Environmental Protection Agency, and WAC Lighting.

The LRC is a leading university-based research center devoted to lighting. LRC conducts research, demonstration, and educational activities on behalf of ASSIST.