what resistor would i need for this accent led?

[theJUDGE]

hello everyone, i just bought a green accent led down the street from my house at radioshack and i dont know what resistor i would need?
it is a simple crystal display for a lightsaber stand, so i bought a 2 AAA battery holder (3 volts), green led, led holder, and a monetary pushbutton switch, but neither i or the worker knew which resistor to use.
the led specs are: foward voltage 2.1 (2.8 max)
30mA
630mcd
supplied with 3volts.

sorry if this seems silly to ask, its just i dont know anything about resistors, and i know that the people of this forum like to help (sometimes at least)

thank you

[Nineteen]

There are calculators on the 'net that can calculate resistors for you. When you find one, bookmark it, as you'll probably be using it a lot.

[theJUDGE]

thank you, i just followed your advice and found my answer. all set now

[Rhyen Skytracker]

The formula is (source Voltage - LED forward Voltage) / LED current = resistance.

Example: You have an accent LED that has 3 volts forward voltage and uses 20mA of current and you are using a 6 Volt battery pack. The formula would be:

(6V - 3V) / .02 A = 150 ohm resistor

[theJUDGE]

that will definately come in handy! thanks guys

[Novastar]

The formula is (source Voltage - LED forward Voltage) / LED current = resistance.

Example: You have an accent LED that has 3 volts forward voltage and uses 20mA of current and you are using a 6 Volt battery pack. The formula would be:

(6V - 3V) / .02 A = 150 ohm resistor

You know what, Rhyen? Until now... it never occurred to me: I should have put this bloody basic formula on the NSCFCDs. D'oh.

Oh well. I guess it's not my job to make sure people understand basic resistance calculations... well, at least not with the CDs. But hmm, I suppose it would have been easy enough to do...