DOE Study: Visual Comfort A Tradeoff for High-Efficacy LEDs

In June, the U.S. Department of Energy (DOE) released the results of a study investigating a group of new LEDs claiming efficacies exceeding 200 lumens per watt (LPW). While all the LEDs performed within 12 percent of their stated efficacies, observers frequently complained of glare and visual discomfort—problems that were more prevalent in products with the highest tested efficacy.

Seven luminaires were selected for the test—five through the LED Lighting Facts listings and two found through an online search. All were industrial luminaires with correlated color temperatures (CCT) of 5,000K, and all but one had exposed LED emitters. Two samples of each luminaire underwent CALiPER photometric testing, and measurements of horizontal illuminance, flicker and maximum luminance were collected. The products were also evaluated by 23 knowledgeable observers.

The DOE found that the LEDs largely performed as advertised. The luminaires lumen outputs varied no more than 9.6 percent from the manufacturer’s claims, and actual power draw varied by no more than 6.8 percent. Efficacies were within 12 percent. CCT and color-rendering index were consistent with claimed values, and all luminaires produced “a fairly even light distribution.”

In contrast to these positive results, the 23 observers rated the luminaires poorly in terms of glare and visual discomfort. The effect these issues had on the observers should not be understated; the three luminaires with the worst overall ratings received the most negative comments about glare. Only two luminaires received acceptable ratings for visual comfort and overall quality—both of which had either diffusing lenses or reflector optics. Plus, the product with the highest rating had the lowest tested efficacy.

There are many important takeaways from this study.

First, users should understand the limitations of the LED Lighting Facts listings. Although the luminaires produced results reasonably close to their efficacy specifications, these tested values were often considerably lower than the information listed in LED Lighting Facts, which are based on the top performers in a product family. As efficacy is affected by lumen output, light distribution, and color temperature, the listings are not straightforward for knowing the efficacy of a specific product.

The study also highlighted the tradeoffs of achieving such high efficiency, namely observers' experience of the product. Although these LEDs are largely performing as promised, visual comfort and glare greatly affect how observers rate a product. To determine the right luminaire for a project, contractors would be best served by testing products and observing their performance in person to determine if the decrease in visual comfort can be ignored to achieve a higher efficiency.

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