The US Department of Energy (DOE) has released an updated report on its lighting evaluation project along the US-Mexican border in Yuma, Arizona, LEDs Magazine reports. In February 2014, DOE installed six LED-based area luminaires on three poles to evaluate their performance in an environment with extreme temperatures and other environmental challenges before proceeding with the complete installation of more than 400 luminaires.
Illuminance measurements were recorded initially in February 2014, and again in September 2014 at about 2,500 hours of operation and in March 2015 at about 5,000 hours of operation.
After 5,000 hours of operation, both the total light output and the distribution of illuminance was found to be changing more rapidly than anticipated. The illuminance values near the poles has increased while the values farther away from the pole have decreased relative to the data recorded when the lights were initially installed. The average horizontal illuminance decreased by 18 percent near the primary fence, and vertical illuminance decreased by 25 percent on the primary fence. The changes in the illuminances occurred after 2,500 hours of operation and persisted after 5,000 hours of operation. There was no measured shift in the color of the light.
The degradation is not due to normal lumen depreciation because such degradation generally results in uniform changes in illuminance, according to the LEDs article. There was also no measured shift in the color of the light over the course of a year and at 5,000 hours of operation.
While the most likely causes for the changes are dirt accumulation combined with possible changes to the luminaire optical elements such as lenses, DOE is planning further investigation to pinpoint the cause. Researchers from Pacific Northwest National Laboratory (PNNL) will conduct thermal simulations of the luminaire and remove one or more of the six luminaires from the site for detailed laboratory analysis. DOE also plans to collect additional data from the site to more fully evaluate possible effects from dirt accumulation and other site-specific effects. Future reports are planned to address these topics.