Nichia 3mm 5mm overdrive / overdriven dead LEDs

Okay, I've searched and read and found some good info about overdriving these bad boys, but I still have a few questions:

1) Assuming NO heatsinking, what are expected life spans for these little guys at 40, 60, 80 mAs? Are there any charts that show current and LED lifespan? I doubt it would be a linear chart right?

2) What exactly happens (visually) when these things "die"? Should I expect a poof of smoke, or diminishing light? I'm sure it depends on the amount of current to the LED.

3) Using say 50 mA and no heatsinking, how long can I expect my LED to last? Are we talking 10 hours, 1,000, 10,000 hours...?

4) How can I tell if I'm getting diminished light from my LEDs. My eyes aren't very sensative, so I wouldn't really notice the difference over time. Am I stuck with holding the one I'm testing next to a new one?

5) I think the answer is no, but is there a multimeter way to check my LEDs for where they are in their life span? I've got a bunch of these guys that I've used for different projects and I don't know if they are still at the top of their game, or ready to be put out to pasture.

Thanks in advance!!!

(Footnote: I modified a taplight for my wife to use to feed the baby at night. I keep finding her using it when the batteries are so dead, almost no light is coming out. I ask her, "Why didn't you tell me it was dying." Her response: "I didn't even notice." I guess she's less sensative to the differences in light than I am!)

Re: Nichia 3mm 5mm overdrive / overdriven dead LED

Try here

Re: Nichia 3mm 5mm overdrive / overdriven dead LED

Ahh... thanks for that link! What a good read! I should have done a search for "degrade" vs. "die"!

So, it looks like:

1) "When overdriven, the led life (to 50% loss) went down fast: to about 500 (hundred, not thousand) hours at 90 mA and about 200 hours at 110 mA."

2) When these things "die", they tend to just get more dim with more heat / current, correct?

3) Using say 50 mA and no heatsinking (BUT using constant current regulation), I'm guessing 5,000 hours?

4) Still wondering, how can I tell if I'm getting diminished light from my LEDs, and/or if it is time to replace them?

Thanks!

Re: Nichia 3mm 5mm overdrive / overdriven dead LED

nerdgineer Thanks for the great link.

Re: Nichia 3mm 5mm overdrive / overdriven dead LED

Graphs in the technical paper referenced above say expected life (to 50%) of white 5 mm driven at 50 mA is about 2000 hours.

Re: Nichia 3mm 5mm overdrive / overdriven dead LED

Uh, unless space is at a premium, why not just use multiple LEDs instead of overdriving them?

Overdriven LEDs can die by strobing - when one of the lead wires seperates slightly from the die and starts expanding and contracting as it makes/loses contact.

Re: Nichia 3mm 5mm overdrive / overdriven dead LED

idleprocess... yeah, I already got the lecture in an email from my buddy Doug Owen. Good advice for sure, if there isn't a limit to space, then I think I'd get a higher ROI with two 20 mA LEDs than one 40 mA LED.

Speaking of the stobe effect. I had two LEDs do this with the first installment of this light:
http://www.nifty-stuff.com/fan-light.php

I had no idea how it happened (until now) and it was pretty darn cool! They should manufacture some LEDs this way!

Thanks for the post!

Re: Nichia 3mm 5mm overdrive / overdriven dead LED

[ QUOTE ]
reviewum said:
3) Using say 50 mA and no heatsinking (BUT using constant current regulation), I'm guessing 5,000 hours?
Thanks!

[/ QUOTE ]

That would be a dream. You'd not even get 10,000 hours at a 25C ambient at only 20mA.

If the flashlight rises above 25C, expect a rapid degredation, even at 20mA.

Above 20mA, expect a much more accelerated drop in light output, even with a 25C ambient.

Combine over driving them above 20mA and a higher than 25C ambient, and you get a really rapid double whammy.

If you PM me with your email addy, I will send you some actual test information that will show you a little more.

Re: Nichia 3mm 5mm overdrive / overdriven dead LED

Ok, that sucks NewBie! Guess living in a country with an average temp of 28-34 deg C doesn't help my LEDs much at all.Worse, I am overdriving them to about 27mA each. Whatever, that's life.