Forward current for assorted LEDs

Question

I have an assortment of T1 and T1¾ LEDs from sampler kits and beginner kits. The kits have sketchy documentation, with missing or inaccurate part numbers. I was able to track down datasheets for some of them, like the “WP7113HD” and the “L934LID.” For others, all I have is a description like “Violet Hi-Br Clear.” So I have several LEDs with a missing or questionable datasheet. It looks like they all of the LEDs expect 2mA, 10mA, or 20mA forward current, but I’m not sure which are which.

Another complication is that some of the datasheets are ambiguous about the intended forward current. For example, the WP7113ID datasheet specifies luminous intensity relative to I_F=10mA, but most of the optical and electrical characteristics are given for I_F=20mA. So even with the datasheet, I’m not sure whether that LED is supposed to be driven at 10mA or 20mA.

How should I choose a forward current for these LEDs? What will happen if I get it wrong and drive a 2mA LED at 10mA, or a 10mA LED at 20mA? I think they are all safe for up to 25–30mA, but I suspect that it’s not a good idea to overdrive them.

Answer 1

Start below 1 mA and observe the light output of the LED. Increase current until light is bright enough for your application, 3-5 mA typical. Non-illumination grade devices won't benefit from currents above ~10 mA so you shouldn't worry about overloading. Another good indicator is the temperature of the leads, when you can feel warmth with your fingers it's time to stop.

Be careful with violet emitters, they could be UV ones and emit just a small amount of visible light. Same for clear which conduct but not emit any light, that's likely IR ones. Old IR may have opaque germanium lens - don't put them in your mouth. Other than that, LEDs are safe to experiment with and quite inexpensive and if you're out of them just salvage some form old electronics.

Take a look at this too -> http://youtu.be/GAriT4B-gkA

Answer 2

I think you are safe in assuming that all those LED's can take 10mA and maybe more. It's mostly a matter of too much heat, so as long as the led is not too hot to the touch you will be OK. (IMHO) As far as the "correct" current. That is your choice, more current is more light, I don't like to have indicator led's too bright so I run them at low current.