LED (Light-Emitting Diode)

An LED (Light Emitting Diode) is a special type of diode that lights up when electricity flows through it in the correct direction.

A diode is an electronic component that lets current flow in only one direction (Anode/Positive to Cathod/negative):

- Anode (+): The positive side.
- Cathode (-): The negative side.

When the anode is connected to a higher voltage than the cathode, the diode allows current to pass through.

If the voltage is reversed, the diode blocks the current.

Polarity

An LED has two pins. The longer pin is the positive side (+), and the shorter pin is the negative side (-). It only works if the positive pin is connected to a positive voltage and the negative pin to ground or zero volts.

Voltage Requirements

LEDs need a certain voltage to turn on. If the voltage is too low, the LED won't light up. If it's too high (more than about 3.3V), the LED might get damaged.

Current limit

LEDs also have a limit on how much current they can handle. Exceeding this can damage them. For example:

- Red LEDs: 1.9-2.2V, max 20mA, recommended 10mA.
- Green and Blue LEDs: 2.9-3.4V, max 10mA, recommended 5mA.

Different coloured LEDs have different voltages, because the voltage needed to light up an LED depends on the material it is made from.

Each LED colour comes from a material with a certain band gap. The band gap is the energy needed to release light when electricity passes through.

For example, blue light has a shorter wavelength than red light, which means it needs more energy to produce.

(the colour of the LED is created at an atomic level inside the LED, not by the colour of it's cover).

Resistor Needed

You cannot connect and LED straight to a power supply. You must use a resistor to limit the current and protect the LED from burning out.

How to use an LED

To use an LED safely and correctly in a circuit:

1. Identify which pin is which: Anode (+) and Cathode (-).
2. Match the voltage: Red LEDs require 1.9-2.2V and Green/Blue require 2.9-3.4V.
3. Use a resistor to limit the current and protect the LED from burning out. Use Ohm's Law to calculate the resistor value (check out the resistor page for how to do this).
4. Connect the LED in the right direction: Connect the anode to the positive side of the power supply through the resistor. Connect the cathode to ground (0V).

A simple circuit will look like this:

Power (+) → Resistor → LED Anode → LED Cathode → Power (-)

5. Turn on the power once the LED is connected correctly with a resistor. The LED should light up.