I've been having trouble with LEDs. I'm running 18 blue ultrabright in parallel. The specs for volts and amperage are as follows:
3.6v typ 4.5v max
20ma typ 30ma max
Each LED has a 220 ohm resistor which was calculated for a 9v source with each LED at 4v, 25ma. This seems well within their range. But, in about a year and a half's time, I've had about 25% burnout. Most of the others are showing signs of intensity and spectrum degradation. Any thoughts as to the cause of this?