Below is a news item I wrote for the October 2018 issue of tED Magazine. Reprinted with permission.
In April 2018, the U.S. Department of Energy (DOE) released its final GATEWAY report documenting the performance of LED luminaires in a high-temperature outdoor lighting environment over four years. DOE’s GATEWAY program, which evaluates projects demonstrating LED capability, studied the results of a retrofit of quartz metal halide area lighting along a 7.2-mile stretch in the Yuma, Arizona Border Patrol Area between the U.S. and Mexico. Temperatures in this area can top 100 degrees Fahrenheit at sunset.
DOE was interested in this project because high-flux lighting, common in street and area lighting and similar applications, can be challenging in an operating environment with high temperatures. DOE wanted to study how this type of environment might affect light output, resulting efficacy, color quality, and service life. The researchers reported a significant decline in light output for the installed first-generation luminaires and color shift for the second-generation luminaires.
In February 2014, three area light poles were retrofitted each with two LED luminaires. Light levels were recorded after 2,500 operating hours (September 2014), 5,000 hours (March 2015), 7,000 hours (September 2015), and 11,000 hours (September 2016). Four second-generation LED luminaires, installed as part of the complete project in September 2016, were tested after 4,000 hours in August 2017.
The new LED lighting reduced energy consumption and maintenance requirements while providing good lighting uniformity—satisfactory results for the Customs and Border Protection. For the first-generation luminaires, however, light levels dramatically declined after 7,000 hours of operation—a 50 percent reduction measured at 11,000 hours. While dirt depreciation was a normal contributing factor, the remainder was due to declining light output.
DOE does not yet know why light output declined so significantly, though an optical issue may have played a part, with Yuma’s high temperatures being the leading suspect. The lesson here is that performance data derived from IES LM-80 may not always be thoroughly accurate predictor of product performance in actual field conditions. And these predictions become even more difficult in extreme conditions such as Yuma’s high-temperature operating environment. DOE called for ongoing improvement of LED system test methods and standards.
The second-generation luminaires installed in September 2016, measured spectral power distribution after 4,000 operating hours showed a variation in color quality (average 152K decrease in correlated color temperature) noticeable on the ground under the lights. The report acknowledged these color differences may not be as noticeable in a more typical area lighting application such as streetlighting, but said it highlights a potential concern when selecting LED luminaires.
Get the report here.
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