Display Lighting

a guest post by Lisa J. Reed, Lighting Designer

The requirements for display lighting – used frequently in retail, but also in restaurant, gallery, or museum applications – differ from general lighting. The shape of the beam, the color of the light, and the color of the objects under the light are more important with display lighting. Now that LEDs are taking over the directional lighting world, we need to understand how LED lamps perform in these important categories.

Display Lighting - diagram

Beam Pattern
A good display light needs to have a definite beam pattern. The brightest part, or the center beam candlepower (CBCP), is the intensity of the brightest part of the beam. The beam angle is the usable part of the beam, defined as the point at which the light intensity falls to 50% of the brightness of that center beam. The part of the beam pattern between 50% and 10% of the maximum intensity is known as field angle. The rest of the light is called spill, and in theatrical lighting field and spill are considered unusable, although they can contribute to the ambient light level in an architectural application. With LED, first make sure the product actually has a measurable CBCP, then inspect the beam for shadows, shape, and watch out for multiple beam circles from the same source.

Color Rendering Index
When illuminating merchandise, it is important that the colors of the products are rendered correctly. Our traditional metric for measuring how well colors are rendered is the Color Rendering Index (CRI), a number from 1 to 100, where 80 is considered good, 90 is great, and 100 is the best. The introduction of LED sources has revealed a few flaws with this metric. Historically CRI has been based on how well a light source renders a series of eight pastel colors. It turns out that LED sources can make those pastel colors look pretty good for a high CRI score while doing a poor job at more saturated colors. New metrics are being explored to better identify how well these new sources render the colors that we see. For today, having a good to great CRI plus a high R9 value (R9 represents saturated red) is a pretty good method of making sure colors look good. If the merchandise being illuminated is high in reds, R9 may become an even more important part of the equation.

Color Temperature
Historically, color temperature has been thought to be a matter of personal preference, but current research may prove that inaccurate. Studies are beginning to show that student math scores improve under cool color temperatures, while they do better at reading and language under warm color temperature light. New research is also showing that alertness and accuracy is increased with cool color temperatures, but warm wavelengths are best for evening and overnight. With LEDs, it is possible to vary the color temperature of a single lamp or fixture. As color temperature research is developed, adjustable color temperatures are sure to become more prevalent.

Color Consistency
Color consistency between fixtures is less important in general lighting than it is with directional lighting. When an entire row of fixtures is all aimed at the same wall, the differences in color are magnified. With LEDs, color consistency – not only at the beginning, but also after the lights have been burning for several thousand hours – is important. Try to get a color warranty from the LED manufacturer for applications where color shift will be detrimental to the design.

Have you used LEDs for directional and display lighting? The opportunity for energy savings in this market is great, because the predominant source used until now has been halogen. Just make sure to get an LED that meets the beam and color requirements for your application.

Lisa J Reed photo - Lighting Blog

Lisa J. Reed has been attracted to lighting (like a moth to a flame) for 20+ years. She is the Founding Principal at Envision Lighting Design, LLC in St. Louis, where she designs, teaches, and writes about architectural lighting. Connect with Lisa J. Reed on Google+.


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