Failure mode of a high power LED with GOOD chips.

Well this is annoying. This LED was a good quality one with well balanced chips. But despite running the 50W LED at just 20W it seems to have developed a stress failure affecting the gold-wire bonds from the chips onto one side of the DC busbar.

I'd guess that the bonding machine may be set to a single bonding current, so it's a delicate balance between not damaging the chips and getting a decent attachment onto the heavier busbar.

This LED would work when first turned on, but gradually the strips would start flashing on and off with some going out completely, until one was left and the light cycled on and off randomly as the LED heated and cooled.