Dimming a LED light
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Determine the voltage of the power source and the forward voltage rating and current rating of the LED being used.
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Determine the required ohm rating of the resistor to be used by applying this calculation: V-Vf/Cf=X, where V is the power source voltage, Vf is the LED's forward voltage rating, and Cf is the LED's current rating and X is the ohm rating of the resistor.
For example, a circuit with a V of 9 volts, a Vf of 2 volts and a Cf of 0.02 amps would result in the equation: 9-2/0.02=350. Therefore, a resistor of 350 ohms would be required to dim the LED. Since resistors only come in certain ohm ratings, a 330 ohm resistor would suffice.