This tutorial covers the fundamentals of LEDs: how they function, how to identify their terminals, and how to safely power them without damaging the component.
Understanding LEDs is essential because they are the standard light source in modern electronics. Used in phones, monitors, custom PC builds, and basic microcontrollers like Arduino or ESP32.
LED stands for Light Emitting Diode. A diode is a one-way valve for electricity: current can only flow through it in one direction. When current moves through the semiconductor inside an LED, it releases energy in the form of photons (light).
Because electricity only flows through a diode one way, plugging an LED in backward prevents it from lighting up.
Anode (+): The positive side. Connects to the positive power source - The longer leg.
Cathode (-): The negative side. Connects to ground (GND) - The shorter leg.
LEDs have almost no internal resistance. If connected directly to a battery (like a 9V or 5V pin), current will surge through the LED instantly, causing it to overheat and burn.
Always place a resistor in series (on either the anode or cathode side) to limit the flow of electrical current.
For a typical 5V circuit and a standard LED, a 220Ω (ohm) or 330Ω resistor provides safe brightness without burning out the bulb.
Find the longer leg (Anode / Positive).
Find the shorter leg (Cathode / Negative).
Put a resistor between the LED and your power source.
Flow current from Positive → Resistor → Anode → Cathode → Ground.