How To Power A LED

Powering an LED is not as easy as simply hooking it up to a battery. An LED has almost no internal resistance. Therefore, if you hook it up directly to a battery, it will burn out quickly as the current flows unimpeded through the LED. You must add a resistor to the LED circuit. This tutorial explains how to calculate the resistance needed.

Step 1

In order to calculate the resistance needed, Ohm’s Law is used. Ohm’s Law can be stated as V = I x R, where V is voltage, I is current and R is resistance. Since we are calculating resistance, we can rearrange the formula to read R = V ÷ I.

Step 2

Plug the values you have into the formula. Performing the calculation will give you the value of the necessary resistor.

Step 3

For example, suppose you have a 12 V supply, a white LED with a forward voltage of 3.4 V, and a current of 20 milliamps (0.020 amps.) First calculate the voltage by subtracting 3.4 from 12, giving 8.6.

Step 4

Now calculate the following: R = 8.6 ÷ 0.020, or 430 Ω (ohms.)

Things Needed

• The voltage of the battery to which you are connecting the LED
• The current to be passed through the LED
• The forward voltage of the LED (found on the LED’s data sheet)

TL;DR (Too Long; Didn’t Read)

If you are connecting LEDs in series, simply add the forward voltages together before subtracting from the supply voltage.