After 18,000 hours of testing 200 sample Philips LED lamps, the US Department of Energy (DOE) reports outstanding lumen and color maintenance for the solid-state lighting (SSL) retrofit lamps. The report "Lumen maintenance testing of the Philips 60-watt replacement lamp L Prize entry" states that the average lumen maintenance is still greater than 100% of the initial average lumen maintenance of the 200 samples.
It was one year ago that the DOE announced that Philips had won the L Prize contest for retrofit A-lamps and a $10 million prize. Earlier this year in April, Philips launched the L Prize winner to the consumer market.
Looking into details of the testing, the lamps were measured at their brightest point about 2000 hours into the testing. It's not unusual for LED sources to get brighter in the early stages of life. The DOE concluded that there has been "very little change" in lumen output over 18,000 hours.
The L Prize documents set a requirement of 70% lumen maintenance over 25,000 hours. Of course that couldn't be proven at the time the prize was awarded. The DOE is now projecting that the Philips lamp will deliver 97.1% lumen maintenance at 25,000 hours.
The L Prize document also included color maintenance requirements. The lamp was to deliver a chromaticity change of less than 0.004 relative to the CIE 1976 color space. At the 7000-hour test point, the Philips lamps stood at a 0.0006 change, and at that point the lamp was declared the prize winner. The 13th worst performing lamp had a chromaticity change of 0.001 at 18,000 hours, well within the limit. The DOE expects 90% of the tested lamps to perform as well or better.
Clearly the Philips lamp design is proving over time that it meets the L Prize requirements. The DOE also notes that the contest has provided "an unprecedented opportunity to test some of the pivotal assumptions about LED lighting products."
The L Prize contest for PAR38 SSL retrofit lamps remains open without an entry. The DOE had temporarily suspended the contest last year, but reopened it with slightly revised requirements this past March.