We had a lively discussion about a year ago about retrofitting LED lighting for 48 inch fluorescents.
Well, I had the first LED fail in the last unit I made. It had flickered a couple times last week, and then went to a dim state. All the LEDs were still lit, so I thought the power supply might have failed. After checking with a meter, the voltage across the whole string was excessive. I used a DVM in diode check mode, and one LED barely lit up. I then powered it back up and measured across that LED, it was dropping 24 V! Amazing it was putting out light and not going up in flames. Anyway, I replaced the LED and all is back to normal.
These CREE LEDs have 3 solder pads on the bottom, anode, cathode and substrate, a thermal conduction path from the diodes. On this one, there was no solder wetting to the center thermal pad. Oops! I have no idea how many more might be like that. I tried to make sure the center pad was wetted, but some probably did not take.
Just thought I'd give a progress report. This unit has been in heavy use in our kitchen since April 2014. The first one of these I did has been running since January 2014.