How to Dim an LED Light

An LED, or light emitting diode, is a small electronic device the emits light when an electrical current passes through it. Because it is a diode, an LED has a positive wire and a negative wire. LEDs are current driven devices. This means that as more voltage is passed through the diode, the current increases and it gets brighter. Reduce the voltage and the LED dims. Placing a resistor to decrease the current flow through an LED will effectively reduce the amount of light the device emits.

Things You'll Need

• Resistor

Instructions

1. Determine the voltage of the power source and the forward voltage rating and current rating of the LED being used.

2. 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.

3. Turn off the power to the circuit you are working on and disconnect the positive wire of the LED from its power wire.

4. Connect the power wire to one wire of the resistor, then connect the resistor's other wire to the positive wire in the LED.

5. Turn on the power to the circuit and observe the change in the brightness of the LED.

6. If the LED is not dim enough, add another resistor, in series, between the first resistor and the LED, to further decrease the current and brightness.

References

• Model Shipwrights' Database: LED lighting for model ships
• Mike's Flight Deck: LED Dimmer