Lifetime and reliability of an LED is a topic that has undergone many revisions of accepted methods to accurately predict the estimated number of usable hours of an LED installation. Since LEDs generally are long life sources of light, combined with the fact that most LED's fail by a defined reduction in output light rather than fail by no light output; measurements have been done to define the amount of light degradation as "end of life". Rating LEDs to a point of 70% or 50% lumen maintenance has been the typical agreed upon end-of-life point. The how and why to get there is typically defined by the LM-80 and TM-21 documentation generated by the Illuminating Engineering Society (IES).
What is Lumen Maintenance?
Lumen Maintenance is an industry standard to determine the lifetime of an LED. As operating time increases, the output of the device will have diminishing returns.
When utilizing a brand-new device, one can define the light output from initial operation as the original output of the device. If we were to utilize an MP-3030-110H-22-80 at typical conditions (65mA forward current) as an example, we can expect a minimum lumen output of 22lm originally. Over time the light output will degrade to a new point. The depreciated light level will then be represented as a percentage of the original light output.
- L90 = 90% of original light output (in this case 19.8 lm)
- L70 = 70% of original light output (in this case 15.4 lm)
- L50 = 50% of original light output (in this case 11 lm)
What is LM-80?
LM-80 is a Lighting Memorandum defining the "Approved Method for Measuring Lumen Maintenance of LED Light Sources". Designed by the IES, this document defines the method utilized to accurately test LED long term performance. Using data collected according to the standard, we can extrapolate an expected lifetime with calculations defined by TM-21. Typically, a minimum sample size of 20 units for each condition is evaluated to 6000 hours using 1000-hour data collection intervals. At each interval the units are tested for lumen depreciation as well as color consistency. Note that there is no pass or fail for the LM-80 as it is a method for evaluating LED Device performance, not for qualifying.
What is TM-21?
The TM-21 is a Technical Memorandum for "Projecting Long Term Lumen Maintenance of LED Light Sources". TM-21 takes the information obtained in the LM-80 procedure and helps to define the expected lifetime for the device under question. Because LED light sources take an extremely long time to degrade, utilizing this calculation method develops a clear picture of the expected LED performance at a certain life stage. Typically, you can extrapolate the lifetime of a device so long as the LM-80 data is within 6x of the testing time. Example: Testing time of 6000 hours can define a device lifetime up to 36,000 hours. Even if the degradation limit does not reach L70, this is the maximum the projection can be defined.
How do I obtain LM-80 reports?
You can request an LM-80 / TM-21 report by sending an email to techsupport@luminus.com. Luminus may choose to provide other forms of data such as a reliability analysis report depending on our target market for specific components.
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