How do I figure out an LED's rating?

[bunyip]

I have 40 nice little blue LEDs, but I have no idea what their ratings are. I would like to figure this out without blowing them out. I have access to a DC power supply/current source and two DMMs.

How do I figure out the optimal voltage/current to run the LEDs at?

[Veland]

If you can find a good multimeter these have a setting for testing led's, giving you the voltage. Mine does, and it's not a very expensive one.. So find/borrow/buy a multimeter and you should be set! As for current, run the led at the voltage found, and measure the current!

good luck!

[Crazy Jayhawk]

Where did you get the LEDs? If they're Radio Shack ones, these are the voltage/current ratings.

Normal blue: 5V, 20mA
Super blue: 3.7V, 20mA

The super blues are a lot brighter than the normal ones and are actually sort of a teal color.

[bunyip]

They're not the Radio Shack ones, I got them from Gateway Electronics for fifty cents each. Figured I couldn't pass up a deal like that.

They seem to be reasonably bright, light teal blue, with a pretty tight diffusion pattern.

Measuring them with a DMM gives me a voltage of 2.5 V, but I'm not really sure what that represents, as I can apply as much voltage across it as I choose. Maybe 2.5 V is the .7 dB cutoff?

It seems like they need more than 2.5 volts anyway. Fooling around with the current source, I've taken the current up to 50 mA and the voltage up to 5V (not simulataneously) with nothing obviously bad happening. But I don't want to blow them out by running them too high for too long...

[Crazy Jayhawk]

I'd put about a 25 to 50-ohm resistor inline with the LED. That way even at 5V the current is limited to 10-20 mA without seriously reducing the brightness of the light.