What is TM-21

Horace He

Last Updated: September 4, 2023

What is TM-21

TM-21 is a term used in the lighting industry to refer to the “Lumen degradation lifetime estimation method for LED light sources” guidelines published by the Illuminating Engineering Society (IES). These guidelines provide a recommended method for projecting the lumen depreciation of LED packages, arrays, or modules based on data collected according to LM-80 testing.

The TM-21 test report is used to estimate the useful life of an LED lighting product under realistic operating temperatures. It utilizes data obtained from LM-80 testing to project the lumen maintenance of an LED source. This projection information is then utilized to estimate the expected lumen degradation of the light source within a complete system or fixture.

The development of TM-21 involved a three-year process by the TM-21 working group (WG) within the IES. The WG explored various options and evaluated mathematical and engineering-based models to provide an effective depreciation fit and a useful projection method. Through their analysis, it was discovered that LED lumen depreciation trends often change after 6000 hours, and there is no reliable and consistent approach to predict these trends from 6000-hour data points. Even a 10,000-hour stream of data is often insufficient to provide statistical confidence in extrapolating a decay curve to large numbers, such as 35,000 hours.

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