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[Reply #30 on:]

Pin 13 led has a resistor. I hope you're joking about not getting it to blink.

Feed a led low enough V and you don't need a resistor but at 5V the lifetime is amazingly short.
Back in the 90's I saw a 555 circuit that ran red leds on very short 9V pulses yet allowed a lifetime of minutes.... it said.... I never tried. The purpose of that one was to make very bright pulses for a fake laser.

if you actually are lucky enough to find a datasheet specific to a generic led, grumpy mike has a bit about it on his site. Boiled down, you can plop some high current through a led for a specific max time and max rate and not kill it.

Thats very handy when your multiplexing as it can help you compensate for off time dimness from an array

[Reply #31 on:]

Not kill it but how about degrade? I've seen 50,000+ hours go by in less than 2 seconds.

[Reply #32 on:]

they must be doing it wrong 

[Reply #33 on:]

For sure. I had a brain fart and turned the pot all the way left to turn the brightness down. That's because left is always less except when less resistance is more current and the led doesn't survive the train of thought before correction is applied. 5V at 0 ohms, meet red led. Ooops.