So what (grin) resistor should i use for this LED then? :D

Community Bar Sport
21

There's voltage regulators and there's current regulators.

Characterizing the Thermal Resistance Coefficient of LEDs

http://www.lrc.rpi.edu/programs/solidstate/cr_thermalresistance.asp

Do LED bubls weaken/lose brightness over time?

But why ask people who have spent more than a little time actually checking these things when you can simply misinterpret a datasheet?

Hmmmm, led brightness drops off over the lifetime (50,000 - 80,000 hours?) by perhaps 30% before it dies. Then the loss is 100%.

So getting old sucks for leds too.

22

someone understands!

Surprisingly, few in the "you have to have a resistor" crowd understand the reason you had articulated as to how a resistor is needed.

23

cjdelphi:

Osgeld:

And bull, any led will dim just by using it, now if its abused it will crap out much quicker than one kept in absolute perfect conditions, but it will still dim

ok, so if i set a spare regulator to a a mid range level until it reads say 15ma, i'll leave it at 2.1v or 2.3v or whatever it is, i'll have an identical one to that i wont touch (only to power it up once to compare brightness), and i'll leave it on for a week and i'll take a before and after picture... don't expect me to do it right now, but I will tomorrow... and i'll see how much visible differences they are

A week? Try 3 months maybe more to get a real drop.

I wonder if leds kept colder than room temp, say in a walk-in freezer, would last appreciably longer, more than 10-12%?

Or what using a led as a light sensor does to its lifetime?

24

be sure to record your current as well over the time. I doubt you will be able to see much in a week without using a lux meter ... but then I tend to design stuff that will last more than a week anyway

let me ask, do you also drive your car with it always in first gear cause it works fine and you see no immediate damage?

25

LOL, you ask about driving a stick in this day and age?
Not that I don't have an abiding dislike for automatics but I'm approaching 60.