How to Determine the Positive Side of an LED

By Mark Stansberry
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Knowing which side of an LED, or Light Emitting Diode, is the positive anode side and which side is the negative cathode side is essential if you want to make the LED emit light. For the LED to emit light, the voltage on the anode must be positive. A simple LED circuit is arranged such that the positive terminal of the battery is connected through a resistor to the anode of the LED. The LED's cathode is connected to the negative terminal of the battery.

Connect the positive terminal of your battery supply to the left lead of a 1,000 ohm resistor. Connect the right lead of the resistor to the left lead of the LED. Connect the right lead of the LED to the negative terminal of the power supply.

Turn on your power supply. Raise the power supply voltage to 1 volt. Observe whether or not the LED emits light. If the LED lights, the positive end, or anode, of the LED is the lead that connects to the resistor.

Continue raising the voltage in 0.3 volt increments if the LED doesn't light. Observe if the LED lights at each 0.3 volt increment until you reach 3.0 volts or the LED begins to emit light. If the LED doesn't light at or below 3 volts, the LED lead that connects to the resistor is the negative lead, or cathode, and the positive end, or anode, of the LED is the lead that connects to the negative terminal of the battery. If the LED does light, the LED lead that connects to the resistor is the positive end of the LED and the negative end of the LED is the lead that connects to the negative terminal of the battery.

About the Author

Mark Stansberry has been a technical and business writer over for 15 years. He has been published in leading technical and business publications such as "Red Herring," "EDN" and "BCC Research." His present writing focus is on computer applications programming, graphic design automation, 3D linear perspective and fractal technology. Stansberry has a Bachelor of Science in electrical engineering from San Jose State University.