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In LED lighting, lumen maintenance is the luminous flux remaining (expressed as a percentage of the initial output) at any selected elapsed operating time. Lumen depreciation is the luminous flux lost over time, and thus the complement of lumen maintenance.
Lumen maintenance compares the amount of light produced from a light source or from a luminaire when it is brand new to the amount of light output at a specific time in the future. For instance, if a luminaire produced 1,000 lumens of light when it was brand new and now produces 700 lumens of light after 30,000 hours, then it would have lumen maintenance of 70% at 30,000 hours. Useful lifetime estimates for LED lighting products are typically given in terms of the expected operating hours until light output has diminished to 70% of initial levels (denoted L70 life).
There are a number of methods for controlling lumen maintenance areas:
- Installing photoreceptors tied directly to ballasts, controlling the voltage output to the lamps based on the set level of luminance.
- Connecting dimming ballasts directly to an energy management system that has been programmed for the expected depreciation of the lamps; the energy management system directs the output of ballasts as necessary to maintain required lighting levels over time.
- Manually verifying lighting levels in a space by using photometers in specific locations, and then manually setting the system to meet lighting requirements.
IES LM-80 is the Department of Energy (DOE) approved testing method for measuring lumen depreciation of solid-state (LED) light sources, arrays and modules. The Illumination Engineering Society (IES) and the Department of Energy Solid State Lighting Standards Development group worked together to create the LM-80 test criteria.
- "Cree Xlamp Long-Term Lumen Maintenance" (PDF). Cree.com. Cree Inc. Retrieved 24 July 2013.
- "LED Reliability and Lumen Maintenance". Retrieved 24 July 2013.
- "Guide to Evaluating LED Lumen Maintenance" (PDF). Retrieved 24 July 2013.
- "Lumen maintenance". ATeam.LBL.gov. Retrieved 28 May 2015.
- "Understanding IES LM-79 & IES LM-80" (PDF). Retrieved 18 July 2015.