The 10W lamp won the DoE's L Prize in 2011 in the 60W replacement category, and at that time Philips said it expected to see lumen maintenance of 97.1 per cent at 25,000 hours - based on 7,000 hours testing of 200 samples.
When the lamps reached 25,000 hours of operation in April this year, the results exceeded expectations. Not only were they still running at 100 per cent lumen output, but the colour was stable (with less than 0.002 change in chromaticity according to the CIE 1976 colour diagram) and all of the lamps survived stress tests which had seen off two thirds of the CFL competitors.
The tests were conducted at the Pacific Northwest National Laboratory, in a specially designed facility kept at 45°C. The DoE's report said the results suggest that lighting manufacturers may be able to get away with diverting attention from testing lumen and colour maintenance, and towards other aspects of product performance.
The Philips lamp on test has since been superseded by lower wattage products designed to last even longer, and without the yellow phosphor outer surface, which proved unpopular.
The report said: ‘As this marks one of the first public opportunities to confirm actual performance of a high-quality LED product at 25,000 hours, it can serve as an indicator for the long-term potential for a well designed and constructed product, and validate the methods being used for extrapolating and predicting long-term performance.’
The DoE said it will continue to test a subset of the lamps, creating what it says will be ‘the only publicly available, third-party data set of long-term LED product operation’.
Its report said: ‘Depending on how the SSL market evolves, how the technology changes over time, and whether buyers and producers coalesce around well-designed products with strong lumen and chromaticity maintenance performance, these test results indicate it might be possible to pay less attention to lumen and chromaticity testing in the future, saving producers and buyers significant money, and allowing them to shift their attention to other luminaire performance attributes.’