[Al Skierkiewicz]

Tom,
In general, calculate needed series resistance on the LED drop of 1.2 volts and 20 ma. If you have high brightness LED or certain blue and white LEDs, the current may be higher. Small, surface mount LEDs will be in the order of 5 to 10ma. You will need to read the specific data sheet for the device you wish to use. Simply subtract 1.2 volts from your power supply to determine the voltage dropped by the series resistor. That voltage divided by .02 (20ma) will give you the resistor value.