Modding Simple LED question

I dont know what resistors i need to buy for some LED's im ordering.

I want a few different colour leds so will that effect the resistors I want?
Ill be running them off 12V.

Also what does (number)mcd mean?

Ive tried them LED calculator things but they just confuse me so could someone help me out?

Thanks

 

mcd = millicandela. It's a measure of brightness per, IIRC, m^3.

If you're dealing with multiple types of LEDs, it's safer to treat each one seperately and have a resistor for each.

 

If you're really, really scared... 470 Ohm is the value I use most.

 

Look at the specs for the LED in question. Find the forward voltage and current. I usually use the typical voltage and current that is listed. Then pull up the nice LED calculator by linear (http://bit-tech.net/article/68) and put in 12 for you supplied voltage and the respective forward voltage and current for the LED. Hit calculate and you should get two different resistor values. The first is the precise value and the 2nd is a typical resistor value you would find. If you can get the first, great - if not you will most likely be able to find the 2nd value. Anything in between should work just fine also. Good luck!

 

Cheers for the replys

I sorted it out last night.

Blue, Green and white - 470 Ohm
Red - 560 Ohm

 

Pretty much any resistor will do yknow... So long as its ROUGHLY in the right area ie 200 - 500ohm... I just pick em up off the ground half the time. Rarely a need to worry about the exact values.