Bad LEDs don’t always die. They just fade away and sometimes rather quickly. Glasgow resident Clive Mitchell, a special effects engineer who uses LEDs in his stage work, sent in this rather amusing example of a large LED clock gone all wrong a few years back:
“This white LED digital clock displaying departure times at the Glasgow Central Station is clearly suffering from LED fade in a large scale manner. The clock, installed in 2005 and subsequently junked, was one of the first uses of low-quality, Chinese white LEDs. Up to this point, the traditional Gallium Arsenide LED had been considered almost indestructible. So it was a real kick in the teeth to a lot of companies when unreliable LEDs hit the market. I, too, got my fingers burned when I used a load for a TV production. Fortunately there were enough in the application to compensate for the ones that failed.”
Low-quality LEDs are something that some manufacturers today admit is problematic, in large part because the design flaws are not evident until after thousands of hours of testing. Manufacturers say engineers should demand to see the data, as I wrote about in an original post at sister publication Electronics Weekly. Read that article and see examples of charts that engineers should use as a reference when purchasing LEDs.