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A primer on LM-80 standard

Posted: 27 Dec 2012 ?? ?Print Version ?Bookmark and Share

Keywords:LM-80? reporting tool? luminaire?

The LED marketplace is usually likened to "The Wild Wild West." Though you're unlikely to see cowboys, cattle or tumbleweed at a lighting tradeshow, the comparison is apt. The market is a seemingly lawless place where outlaws are free to roam unpunished, releasing products to the market that may or may not live up to their stated performance and lifetime claims.

At the same time, government agencies, lighting standards organisations and major manufacturers are attempting to tame the market by adapting LED best practices from other industries, such as the automotive and semiconductor industries, which have long-term experience with the technology. The intent here being to implement standards that enable lighting professionals to easily evaluate and compare LED components, lamps and luminaires. (In other words, to "civilize" the Wild West.)

What is LM-80?
The LM-80 is one such standard. LM-80 refers to a method for measuring the lumen depreciation of solid-state lighting sources, such as LED packages, modules and arrays. Before the advent of LM-80, LED component manufacturers each reported lumen maintenance data using their own disparate and varied systems. To avoid customer confusion, members of the Illuminating Engineering Society (IES), including members from Philips Lumileds, came together to create a standard methodology that would allow customers to evaluate and compare the lumen maintenance of LED components from different companies. LM-80 was born.

LM-80 can be a useful tool for lighting professionals who are looking to analyse LED products; however, it is not a measure of LED system performance or reliability. It only describes how to measure how one part of an LED luminairethe LED light sourceperforms over a period of time and under certain set conditions. Other components, including the LED optical system, heat sink, LED drivers and luminaire housing, should also be taken into consideration to form a full picture of an LED luminaire's projected useable life. LM-80 is merely one critical part of a larger puzzle. LM-80 is also not a measure of the "lifetime" of a component or the LED lamps and luminaires that use that component. Unfortunately, LED component, lamp and luminaire manufacturers, among others, often use the data found in an LM-80 report to substantiate the "lifetime" claims of an LED product, even though that data alone cannot be used to predict the useful life of an LED product or system.

Figure: Samples of data from a Philips Lumileds LM-80 test report, showing light output over time for the same LED. The first graph show results of the LED tested at 350mA and the second graph at 500mA.

What LM-80 can do for you
While LM-80 doesn't provide a full picture of a LED component's long-term performance, it is an important part of the equation. Luminaire and lamp manufacturers, lighting designers and researchers should know how quickly the light output of an LED will depreciate to help them determine the useful lifetime of the product in which the LED will be used. They should also look at how the LED's light output has degraded under the various temperature and current conditions, as well as how the colour point has shifted at those same conditions. Those measurements will enable them to assess how the LED component is expected to perform under similar circumstances.

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