Below is a news item I wrote for the November issue of tED Magazine. Reprinted with permission.
The seven pairs of high-efficacy LED luminaires installed in a mockup for evaluation. Image courtesy of DoE.
In 2017, the U.S. Department of Energy (DoE) evaluated the performance of a selection of LED lighting products with very high published efficacies close to or topping 200 lumens/W. All seven were industrial luminaires, with all but one featuring unshielded light emitters.
DoE set out to validate the efficacy claims, characterize commonalities between the products, and identify any performance tradeoffs. Pairs of product samples for each of the seven luminaires were tested for horizontal light level, flicker, and maximum luminance (photometric brightness). Further, 23 knowledgeable observers visually evaluated the products in a mockup.
The resulting report was published June 2018.
Efficacy. Light output deviated no more than 9.6 percent and wattage no more than 6.8 percent, while efficacies varied as much as 12 percent from published values. Tested values were often lower than those listed in LED Lighting Facts, which is generally based on best performers in a product family, demonstrating that performance variation in product families is not uncommon.
Light distribution. All luminaires in a mockup high-bay installation emitted light in a reasonably uniform pattern across the task plane, with a maximum-to-minimum light level ratio below 1.7 at a task height of 37 inches off the floor.
Flicker. One of the seven luminaires demonstrated flicker exceeding the Institute of Electrical and Electronics Engineers’ (IEEE) low-risk criteria as defined in Standard PAR1789-2015.
Color quality. Photometric testing showed correlated color temperature (CCT) and color rendering index (CRI) ratings that were in line with manufacturer claims. All seven tested products featured a CCT of 5000K, not surprising as the highest efficacies generally correlate with higher CCTs. Among the tested product types, reducing CCT from 5000K to 3000K produced as much as a 17 percent efficacy reduction.
Photometric brightness. Direct luminance for the exposed LEDs ranged from 154,000 to 478,000 candelas per square meter. One luminaire featured a diffuser that softened luminance to 40,000 cd/m2, a luminance 1.6 times higher than a T5HO fluorescent lamp.
Visual comfort. The most frequent complaint amount the study’s 23 observers was glare, perhaps not surprising given the very high luminances of the products. Only two of the seven products were rated as acceptable for visual comfort and overall quality. These products featured either a diffusing lens or reflector optics that cut off view of the exposed LEDs above a set viewing angle. Both were rated as acceptable for light distribution, shadows, and colors as well as visual comfort. The three lowest-rated products had the most negative complaints about glare.
We can learn several things from this. First, there are LED products that are reaching extraordinary levels of efficacy, though one’s mileage may vary within a product line, especially if there is a choice of CCTs. Next, besides efficacy, other factors such as visual comfort, uniformity, flicker, shadows, and color quality should be given due weight based on the application needs, keeping in mind there may be a tradeoff between efficacy and visual comfort. Ideally, a product under consideration should be evaluated in a mockup before installation.
Get the DoE report here.
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