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LED Lumen Maintenance and Light Loss Factors

An article has been published in IES LEUKOS entitled "Lumen Maintenance and Light Loss Factors: Consequences of Current Design Practices for LEDs." The article was written by Michael Royer of Pacific Northwest National Laboratory and discusses complications related to the lamp lumen depreciation (LLD) light loss factor and LEDs. Because of the unique operating characteristics of LEDs and lack of a comprehensive lifetime rating—as well as the problematic relationship between SSL lifetime and lumen maintenance—determining an appropriate LLD factor for LED products is difficult. The IES recommends using an LLD of no greater than 0.70 when the quantity of light is an important design consideration. The article discusses the issue in detail, compares the performance of some conventional and LED products, and examines alternatives to the currently recommended approach for determining LLD factors for LED products. Access at: