Product Selection Guide Page 1115 Product Selection Guide-11th Edition

1115 PRODUCT INFORMATION Life & Depreciation LED TECHNICAL INFORMATION PSG11 TECHNICAL INFORMATION As can be seen, life (defined by the time at which light degrades to 70% of initial lumens) is significantly shorter for the luminaires with poor thermal management. In order to ensure that LED suppliers measure and report the lumen maintenance characteristics of their LEDs in a consistent way, the Department of Energy (DOE) engaged the support of IES to establish the LM80 Standard. This test method requires LED suppliers to test and report the LED's lumen depreciation values at three operating conditions (two set within the document, and the third at the manufacturer's discretion) over a period of 6,000 hours. This establishes a standard test methodology that (along with the LED spec sheets) allows luminaire companies to compare performance across LED suppliers. The LM80 does not prescribe how to extrapolate this 6khr data to the life predictions of the LED. This task has been left to another standard, titled IES TM21, which takes LM80 data and uses an exponential curve fit to project the point at which lumens depreciate to 50%, 70% or any other desired point. Hence, it is very important for the luminaire manufacturer to understand the specific extrapolation methods used by their chosen supplier and how the luminaire design impacts these critical parameters. In turn, manufacturers must process and supply the relevant results of this analysis (life of the luminaire, temperature limitations, etc) to customers for their consideration in selecting an LED lighting system. Operating Hours T hreshold T ime 70% T emp light output A good discussion of the useful lifetime of LEDs can be found at the Department of Energy's website in a paper entitled "Lifetime of White LEDs". ssl/factsheets.html

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