How to Design an LED Light
- 1). Use Ohm's Law to find the value of the minimum resistance R for use with an LED. The general formula for R is (Voltage Source -- LED Voltage) / LED Current. For a current of 25 milliamps, R is (3V -- 1.9 V) / 0.025 = 44 ohms. A standard resistance value of 47 ohms or more should be used.
- 2). Create a series circuit with the AA batteries, 47-ohm resistor, and LED. Attach the battery holder to the breadboard. Do not place the batteries inside at this time. Using jumper wires, attach one end of the resistor to the holder's red lead.
- 3). Insert the LED into the breadboard. Wire the LED's positive side to the free end of the resistor. The positive side usually has a lead that longer than the negative one.
- 4). Connect the negative side of the LED to the black wire of the battery holder, which is ground. Place the batteries inside, and the LED will light up and glow steadily.
