With new LED lighting products appearing on the market at record speed, the need for industry standards around quality, performance and measurement is more pressing than ever. Standards provide a level playing field for manufacturers, and they provide confidence for customers who previously faced inconsistent product claims and metrics based on no common denominator. In particular, standards for the measurement and projection of LED lifetime will elevate the game by setting proper expectations in the market. (Contrary to urban myth, LEDs don’t last 100,000 hours across the board!)
I briefly addressed the subject of LED lifetime last Fall, and have since authored a detailed white paper, accessible here. With the establishment of a new IES standard, known as TM-21, the industry has taken another big step towards one consistent and reliable model for LED lifetime calculation.
What is TM-21? It first helps to understand LM-80, which is the IES-approved method of measuring the lumen maintenance of LED packages and modules. Lumen maintenance refers to the number of hours that a light source remains “useful” before its output diminishes to 70%. The creation of the LM-80 standard ensured that manufacturers were testing for lumen maintenance in a consistent fashion – requiring a minimum of 6,000 hours of testing at various temperatures. The lumen maintenance measurement, known as L70, would then be extrapolated from these test results. However, before the arrival of TM-21, there was no standard basis for the extrapolation, and calculations varied from one manufacturer to another.
Simply put, the TM-21 standard picks up where LM-80 left off. Since LED sources are capable of lifetimes well beyond 6,000 hours, TM-21 establishes a standard way to use LM-80 data to make consistent lifetime projections beyond the testing period. TM-21 dictates which values can be used in the calculation based on the sample size, number of hours and intervals tested, and test suite temperature. It also puts a cap on the extrapolation – a maximum of 6X the hours tested – which eliminates those infamous 100,000-hour claims of yesterday. Since most manufacturers test for 6,000 or 10,000 hours, the accurate range based on TM-21 is up to 36,000 to 60,000 hours of useful life. After this time period, it does not mean the LED will fail; it is just the limit that can be claimed when using TM-21.
While these industry standards have provided tremendous help, there are other factors that must be considered when estimating the lifetime of integrated LED fixtures – vs. the LED packages or modules alone. The design of the fixture is critical, from the drivers and optics to thermal management, in addition to the fixture’s intended application and operating environment.
The bottom line when it comes to LED lifetime is to do your homework and know your manufacturer. Ask about their testing practices and adherence to standards. Those of us in the industry who take great care to deliver quality products with substantiated data will always be happy to answer.