Lighting plays an important role in supporting retail operations, from attracting customers to influencing product appearance to corporate branding. A recent survey of lighting designers and specifiers by the National Lighting Product Information Program showed that, for retail applications, light source color properties are considered more important than any other light source criterion, including energy efficiency.
To define light source color properties, the lighting industry predominantly relies on two metrics: correlated color temperature (CCT, which is commonly used as an indication of the apparent “warmth” or “coolness” of the light emitted by a source), and color rendering index (CRI), which is an indication of the light source’s ability to make illuminated objects appear natural.
However, these two metrics, developed in the last century, are facing increased challenges and criticisms as new types of light sources, particularly LEDs, become more prevalent.
To help retail lighting designers better understand CCT and CRI, and choose the best lighting product for specific retail applications, the Alliance for Solid-State Illumination Systems and Technologies (ASSIST) published a new volume in its ASSIST Recommends series.
Recommendations for Specifying Color Properties of Light Sources for Retail Merchandising recommends two-metric approaches for specifying light sources to achieve desired color appearance of the illumination, as well as good color rendering in retail applications.
For example, to meet the expectations for good color rendering in retail applications, ASSIST advises using the well-established CRI along with another metric: gamut area index (GAI). GAI represents the relative separation of object colors illuminated by a light source; the greater the GAI, the greater the apparent saturation or vividness of the object colors, according to Mark Rea, director of Rensselaer Polytechnic Institute’s Lighting Research Center and co-author of the publication.
Practical, step-by-step methods are included in the publication for the two-metric color rendering approach described here, as well as a two-metric approach for achieving consistent results in desired color appearance of the illumination.
The two new ASSIST Recommends publications are available for free download from the ASSIST: www.lrc.rpi.edu/programs/solidstate/assist/recommends/lightcolor.asp.