LED

A light-emitting diode — a diode that emits light when current flows through it in the forward direction.

Symbol: IEC 60617 (diode symbol + light arrows)

How it works

An LED is a diode built from a semiconductor that emits photons when electrons cross its junction. Like any diode, it only conducts in one direction and has a forward voltage drop — but that drop depends on the LED's color, since color corresponds to the semiconductor's bandgap energy (red and infrared LEDs have the lowest forward voltage, blue and white the highest).

Because an LED's resistance drops sharply once it starts conducting, it must always be paired with a current-limiting resistor — connecting one directly across a supply voltage higher than its forward voltage will destroy it almost instantly.

CircuitForge lets you set the forward voltage directly, which is the one parameter that changes between LED colors in the simulation.

Key Formulas

Series Resistor CalculationR = (V_supply - V_forward) / I_desired

Common Mistakes

Assuming all LEDs have the same forward voltage. Swapping a red LED (Vf ≈ 2.0V) for a blue LED (Vf ≈ 3.2V) in the same circuit will drastically reduce the current, often leaving the blue LED too dim to see.

Common Variants

5mm Red LED

The lowest forward-voltage common LED — the standard first component in beginner circuit kits.

5mm Blue LED

A higher forward-voltage LED that needs more supply headroom than red or green — a common gotcha when swapping LED colors in an existing circuit.