By Mark Stansberry – Updated Mar 24, 2022
Identifying the correct polarity of an LED—anode (positive) and cathode (negative)—is vital for ensuring the diode emits light. The LED will only light when its anode is connected to a more positive voltage than its cathode.
Connect the positive terminal of your power supply to the left lead of a 1 kΩ resistor. Attach the right lead of the resistor to the left lead of the LED. Connect the LED’s right lead to the negative terminal of the power supply.
Power on the supply and set the voltage to 1 V. Observe whether the LED lights. If it does, the lead attached to the resistor is the anode.
If the LED remains dark, increase the voltage in 0.3 V steps until you reach 3 V or until the LED illuminates. If it still does not light, the lead connected to the resistor is the cathode, and the other lead is the anode. If it lights at any point, the lead connected to the resistor is the positive end.
You can quickly determine the positive lead of an LED. The shorter pin is usually the anode, but if it has been cut, examine the internal electrodes or consult the manufacturer’s datasheet for a diagram.
Improper use of electronic equipment can lead to fire, serious injury, or death. Always work under the supervision of a certified electronic technician or engineer, and obtain an electronic safety certificate before handling components.
