Typical Forward Voltages of LEDs

[healthyfatboy]

I just got my 100 LED's from China that I bought off of e-Bay. Now, they didn't come with anything and the ad didn't have much about the specifications at all so I thought I would get some generic numbers from people. What are the typical forward voltages and currents for these color LED's?

White

Blue

Red

Green

Thanks for your help everyone! This place is a great resource.

[anatoly]

The ebay ad should have had some kind of specification as to voltage, otherwise it makes it difficult to pick out your resistors. Some of those companies include resistors for 12v power, but if you use 5v receiver power like I do then that won't work very well. Last time I bought white LEDs on ebay they were 3.6v, so for 5v power I got 82 ohm resistors for a 20mA amp draw per LED. The LEDs you get at Radio Shack, by comparison, are usually around 2.4v and would require a 150 ohm resistor for 5v power if wired in parallel.

[MorrisM]

You should get the forward voltage and current specs from your supplier to be sure, but here are some specs that will work with most leds at 20mA.
Remember to use a higher value resistor if you can't get the exact value for your LED. The resister value is not critical. I doubt you could see the difference if you used a 150 ohm instead of a 82 ohm.

blue, white, green: 3.2 to 3.7 forward volts
5V=82 ohm....12V=470 ohm

red, yellow: 1.9 to 2.2 forward volts
5V=180 ohm ...12V=560ohm

EDIT: you may use this data as you wish, but there is no guarantee on its suitability for your particular LED. Use it at your own (and the LED's) risk. :)

[jasmine2501]

They should be marked in some way or there should be a list on the site or something. Otherwise it's gonna be hard to figure out. You could hook them up to your power source and try different resistors until you get 20 milli-amps, which most of them run at, but without specs, you can't be sure that they will handle that.

MorrisM posted some examples, but I have bags of LEDs here with much higher numbers... my red ones are 2.8V, blues 3.4V, white 3.6V... but he is correct about the resistor values. The calculator may indicate that you need 100 ohms, but if you use 75, you'll hardly notice the difference. They will be ok as long as they don't go over their amperage limit.

[healthyfatboy]

I did get some values from the manufacturer on e-Bay and they seem to work just fine at 20mA. They're pretty bright as well.
With school starting up this week, it will take some time before I can get to soldering a bunch of LED's for my SS but I am the lab TA so if there's a soldering iron in there, I can just do it while people don't have questions! Great!