LED resistance?

[Super_Ted01]

i wanna get some led's hooked up, but im not sure what resistors to use, heres the led's http://www.maplin.co.uk/Module.aspx?ModuleNo=-11200&criteria=Ultra%20Bright%20LEDs&doy=3m9
i was plannin on usin a 12V supply from a molex connector.
help and suggestions much appreciated

[dgrmkrp]

use the 5v from the molex :) u can use a 100ohm res in series if the led is a 3.3V one... or if u have ultrabright leds (that are rated for 5V) use 5V and see if the "legs" heat up or not.. if they do, u need the resistor.. if the led burns.. i'm sorry:rolleyes: .. common values are 470ohm for a 12V step down and 100ohm for 5V step-down... experiment with cheap parts :)

[chedabob]

that might explain why my leds in my xbox got red hot : i put them on the 12v line instead of the 5v line, with just a 100ohm resistor :P

[cybertron]

This is what I've been using to figure out resistors for my LEDs: http://www.thebestcasescenario.com/forum/showthread.php?t=642