LED Indicators
When using a Light Emitting Diode (LED) as an indicator, use the following formula to determine series resistance for various voltages: R = (E - 1.7) x 1000/I, where R is the resistance in ohms, E is the supply voltage (DC) and I is the LED current in milliamps.
Eg. to operate the LED at 20mA, for 6V, use 220 ohms
9V - use 390 ohms.
12V - use 560 ohms
24V - use 1.2k ohms
Pasted from <http://www.dse.com.au/cgi-bin/dse.fi...ogs/SUP1000058>
Good candiadate