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How to Test LEDs

Light-emitting diodes, or LEDs, were first introduced in 1962 as semiconductor light sources. Unlike incandescent lamps, LEDs operate very efficiently and produce less heat. The use of LEDs for lighting purposes has grown in recent years. Examples of LED applications include aircraft navigation lights, automotive signal lights and flash lights (See References 1). Anyone can easily test a LED for proper operation, regardless of whether the LED is installed in a circuit.

Things You'll Need

Multimeter
9-volt battery
Jumper wire
1K ohm resistor

Instructions

Testing an LED in a circuit
- 1
  Turn off and unplug the device that powers the LED.
- 2
  Turn on your multimeter. Set the range selector knob to the "Diode Test" setting.
- 3
  Test the LED by placing one of the multimeter's test leads on each LED lead.
- 4
  Read the voltage. If the voltage is greater than 3 volts, the LED is faulty. If the reading is "OL," switch the test leads. Measure the voltage again. A properly functioning LED should display a reading of 3 volts or less (See References 2)
Testing an LED out of a circuit
- 5
  Connect a 9-volt battery's positive terminal to one end of a 1K ohm resistor. Use a wire jumper to make the connection.
- 6
  Touch one of the LED leads to the other end of the 1K ohm resistor. Touch the other LED lead to the battery's negative terminal.
- 7
  Observe the LED. A properly functioning LED will be lit. Switch the LED leads if the LED is not lit. Observe the LED again. A faulty LED will be dark in both cases (See References 3).

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