

In most circumstances (unless specifically stated by an IC specification), an LED must have a resistor in series with it to prevent it destroying itself.*
For voltages between 6 to 12v, a 470 ohm resistor will be fine but to get maximum brightness, without damaging it, you should work out the correct value.
This will depend on
 The forward voltage (VF) of the LED
 The forward current (IF) of the LED
 The voltage Vin.
To work out the resistor do the following:
 Subtract the forward voltage (usually 2 to 4v) from the Vin,
 Divide the result by the LED current.
So if Vin =12v, VF = 2v and IF = 30mA then R1 would be
= (Vin  VF) / IF
= 12v  2v) / 0.03 = 333 ohms, or 330 ohm resistor
*You can match the LED voltage exactly thus eliminating the need for a series resistor, but this is a risky practise keeping the voltage exactly right, especially if driving a display of LEDs. The outcome can be catastrophic.




