"The other test […] is purely a life test," he added. "And in our category that test is run for 6,000 hours, so it's effectively nine straight months of testing." Life test is a useful if loose euphemism for what the test actually measures, which is lumen depreciation: the extent to which the lamp's light output falls over time.
"All LED lights at some point are going to start losing the amount of lumens that come out of the light," Rosenfield said. "The industry has set a number, called L70, which basically represents 70 percent of the original light output, as the end of life for an LED." So, the industry defines an LED light bulb as dead when its output falls to 70 percent of what it was to begin with.
The problem, Rosenfield explained, is that LED light bulbs haven't been around long enough for the industry to have a good understanding of how their performance degrades over time. Instead an algorithm is used which, after 6,000 hours of testing, projects the number of hours remaining before the LED will reach L70. The 25,000-hour rated life of Switch's and other LED products has not been tested in full because doing so would take nearly three years. Instead this number is a projection based on the algorithm used. Even so, it's still a test that takes a significant amount of time. Depreciation, by the way, is non-linear, and light output can at times increase as well as fall away, Rosenfield explained.
There is a semi-shortcut, though. LED light bulbs are effectively electronics packages in which the LEDs are but one type of component. Being solid state lighting products themselves, the LEDs are eligible for testing under IES LM-80. If Cree, one of the LED manufacturers Switch has used for its bulbs, has its LEDs tested to 6,000 hours, Switch doesn't have to repeat the entire test. Switch's product can instead undergo a 3,000-hour (4.5-month) test to check that depreciation follows the expected pattern. "It's still an advantage to test for the entire 6,000 hours because we may be able to run longer than what the LEDs actually are claiming," Rosenfield said.
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