**LED**s (Light Emitting Diodes) must always be operated with a resistor in series to limit the current to a safe level. Most LEDs can only tolerate a current of about 30mA maximum. To calculate the resistor value required the forward voltage (V

_{f}) and current (I

_{f})of the LED must be known. These can be found from the suppliers catalogue. For standard LEDs V

_{f}is about 2V and I

_{f}is about 20mA.

The resistor value can be calculated as follows:

R = (V

_{s}- V

_{f}) / I

_{f}

= (Supply Voltage - Forward Voltage) / Forward Current

Note that I

_{f}is in Amps,

__NOT__Milliamps! (20mA = 0.02A)