This article is an excerpt of a document entitled Lighting Facts FAQ which deals with LED Lumen Maintenance and Warranty Label Changes.
LM-79, LM-80 and TM-21 are standardized documents that list recommendations on the assessment of maintenance of the luminous flux for LED-based lighting. What differentiates one from the other? How can these documents impact your lighting choices?
LM-79 is an approved process that measures the electrical and photometric properties of LED products. This process includes luminous flux, electrical power, efficiency, chromaticity as well as the diffusion of luminous intensity. Results of all five metric measurements displayed on a lighting product label originate from test results based on the LM-79 record.
LM-80 is an approved process that measures the maintenance of the luminous flux for a group of electroluminescent diodes (LED) at various operating temperatures. This document recommends testing over the course of a minimum of 6,000 hours (it is stated, however, that a testing period of 10,000 hours is advisable); measurements are taken at 1,000-hour intervals. Beyond those specifications, LM-80 offers no other determination or estimate as to the lifespan (or maintenance of luminous flux) over and above the number of test hours. Despite 10,000-hour testing time slots, recommendations do very little to challenge assertions made by LED-based lighting manufacturers regarding the lifespan of LED products sold on the market today.
TM-21 provides guidelines on the use of data compiled through LM-80 tests to assess the lifespan of a light source beyond the number of test hours recommended by LM-80; TM-21 allows us to deduce the lifespan up to six times the number of test hours. For instance, diodes tested for 6 000 hours in a laboratory setting should not be sold with an endorsement stipulating a lifespan greater than 36,000 hours based on the L70 lifespan.
Both LM-80 and TM-21 results have been designed to be assessed together, as TM-21 uses test data provided by LM-80 with data obtained further to operating temperature performance in order to predict the maintenance of luminous flux of LED-based lighting.