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.
How this component 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.
Deep Dive: 5mm Blue LED
Blue LEDs are a much more recent invention than red or green ones, relying on indium gallium nitride (InGaN) semiconductors. This material has a high bandgap energy required to emit high-frequency blue photons (~465nm). As a direct physical consequence, blue LEDs require a much higher forward voltage (Vf) to turn on — typically between 3.0V and 3.4V.
This high voltage requirement completely changes how blue LEDs must be designed into low-voltage circuits. For example, if you attempt to run a blue LED directly from a 3.0V CR2032 coin cell, the supply voltage is below the typical 3.2V threshold. The LED might glow very dimly as it barely overcomes the barrier, but it will not reach full brightness. On a standard 5V system, the voltage drop across the current-limiting resistor is much smaller than with a red LED (5V - 3.2V = 1.8V), so a smaller resistor (e.g. 100Ω) is needed to achieve the same 20mA current.
Additionally, blue LEDs have remarkably high perceived brightness and energy efficiency. Because modern blue InGaN chips are so efficient, running them at the "standard" 20mA is often blindingly bright for an indicator light. In many modern designs, blue LEDs are intentionally under-driven at just 1mA to 5mA (using a 1kΩ or 2.2kΩ resistor on a 5V supply) to produce a comfortable glow.
Common Use Cases
- Status indicator on circuits with at least 5V of supply headroom
- Component in an RGB mixing demonstration alongside red and green LEDs
- Demonstrating why forward voltage matters when swapping components in a fixed-resistor circuit
Frequently Asked Questions
Can I swap a red LED for a blue one with the same resistor?
Only if your supply voltage has enough headroom above blue's ~3.2V forward voltage — on a 3V coin-cell circuit sized for a 2V red LED, a blue LED may barely light or not turn on at all. Recompute the resistor for the new forward voltage.
Why do blue LEDs often seem dimmer at the same current?
Perceived brightness depends on both output power and the eye's sensitivity curve, which peaks in green — so equal electrical power doesn't mean equal perceived brightness across colors.
Comparison Notes
Compared to a standard red LED, the blue LED demands a much higher forward voltage (3.2V vs 2.0V), making it poorly suited for 3V or 3.3V logic circuits without dedicated driver transistors. However, modern blue LEDs are vastly more efficient, meaning that while a red LED might require a full 20mA to act as a visible indicator, a blue LED can often provide the same perceived brightness using only 2mA to 5mA.