Halloween was over a month ago with the winter holiday season already under way. In the tradition of “The Nightmare Before Christmas”, let’s talk about scary TM-21 calculations.

As you may know, the IES has published the TM-21-11: Projecting Long Term Lumen Maintenance of LED Light Sources. LED light sources provide a very long usable life, but light output gradually depreciates over time. TM-21-11 provides the method for determining when the “useful lifetime” of an LED is reached, a point when the light emitted from an LED depreciates to a level where it is no longer considered adequate for a specific application. Lumen maintenance of LEDs can vary from manufacturer to manufacturer and between different LED package types produced by a single manufacturer. 

This is great! Now there is an established method that manufacturers can use to extrapolate the lumen maintenance or L70 (end-of-life) on their LED fixture/lamps. Unfortunately, it does nothing to address the life of the power supply, driver or color maintenance of the LEDs. 

There have been several recent claims of 100,000 hour L70 for white PC LEDs by manufacturers of late, attributing TM-21 calculations for these results. And they are most likely right. Their LEDs will produce more than 70% of their initial light output at over 100,000 hours. But can the power supply or LED driver last that long? To their credit, they have made no such claims, but neither have they made this a point of discussion. So the average consumer/end user will assume that the entire LED fixture/lamp will last the predicted 100,000 plus hours. 

Sounds like it will be a rude awakening for a lot of people in a half a decade or more. This is a scary thought.