TM-21 is the Illuminating Engineering Society of North America (IESNA) approved method for taking LM-80 data and making useful LED lifetime projections. The standards apply to lifetime projection of LED package, array or module alone. The results can then be used to interpolate the lifetime of an LED source within a system (luminaire or integrated lamp) using the in-situ LED source case temperature.
Who can perform testing?
There is not such a thing as testing, it is a mathematical method based on LM-80-08 collected data.
Among other thing, TM-21-11 will consider:
– If total LM-80 data period is between 6,000 and 10,000 hrs, we consider the last 5,000 hours
– If total data period is above 10,000 hours, we use the last half of collected data
– In situ case temperature interpolation using Arrhenius equation between LM-80 temperature
– Projections are limited to 6 times the available LM-80 data period so projected and reported lifetime may or not be the same
What does it provide?
The method will provide a projected lifetime for the LED source or system.
Life notation results will then use the following standardized nomenclature: Lp (Yk)
– P: Lumen maintenance percentage. For LED luminaire we consider L70 to be the standard. After 30% lumen depreciation, we consider the system is not performing its duty anymore and should be replaced (see Lifetime section of Lighting Guide for more details)
– Y: Length of LM-80 data period in thousands of hours
Example: L70(6k) = 36,000 hours