The Illuminating Engineering Society of North America (IES) recently introduced a new document, TM-21-11, "Projecting Long Term Lumen Maintenance of LED Light Sources." The document recommends a method for projecting the lumen maintenance of LED light sources from the data obtained by the procedures found in IES document LM-80-08, "Approved Method for Measuring Lumen Maintenance of LED Light Sources."
LED light sources provide a very long usable life but light output gradually depreciates over time. TM-21-11 provides the method for determining when the “useful lifetime” of an LED is reached, which can vary from manufacturer to manufacturer and between different LED package types produced by a single manufacturer.
TM-21-11, "Projecting Long Term Lumen Maintenance of LED Light Sources," is available on the IES website at www.ies.org/store. Phone orders can be directed to 212-248-5000, ext 112.