THE LED

LED stands for Light-Emitting Diode. An electronic component that produces light when electricity flows through it (in the right direction).

To understand how it works we need to shrink down to the size of an electron (if you’ve forgotten what an electron is – click here).

HOW DOES AN LED PRODUCE LIGHT?

Inside the LED is a semiconductor chip. A semiconductor is not a conductor (like copper that allows electricity to flow) nor is it an insulator (like rubber that does not allow electricity to flow). Instead it conducts electricity only under certain conditions.

The chip is like a sandwich made from 2 different types of “bread” on the top and bottom. There is an n-type layer and p-type layer. The n-type layer is crammed full of extra electrons and the p-type have holes, or want more electrons.

When a forward voltage is applied (the special condition that makes it conduct) electrons move toward (and across) the barrier from the n-side, holes move toward (and across) it from the p-side, and they join. This recombination is what produces the light. When an electron recombines with a hole, it drops to a lower energy state and releases that extra energy as a photon (light).

A simple analogy: Think of the junction (where they meet) as a “party zone” in the middle. Forward bias opens the doors wide, so electrons rush in from one side and holes from the other — they meet in or near that central zone and “pair up,” releasing light as they do!

Confused about moving holes? Imagine a theater row almost full of people (electrons), but one seat is empty (a hole). If someone stands up and moves one seat over to fill the empty seat, now the empty seat is where that person came from. It looks like the empty seat moved backward, even though only people shifted. That’s how holes ‘move’ — electrons shifting makes the empty spot appear to travel!

How do we get different colours?

Using different semiconductor materials or mixes of materials produces different coloured light.

When the electron and hole recombine the electron drops down that energy step and releases a specific amount of energy as a photon (light particle).

A bigger energy drop → higher energy photon → shorter wavelength → bluer/violet light.
A smaller energy drop → lower energy photon → longer wavelength → redder light.

The color comes from how big/steep the “drop” (energy gap) is — bigger drop = bluer light, smaller = redder.

If you are struggling to understand then try and picture this:

Imagine electrons are excited kids at the top of a waterslide — crowded and full of energy (that’s the n-side of the LED). Down below is a pool with empty spaces waiting (holes on the p-side).

Normally there’s a barrier, so they can’t slide down. But when you connect the battery the right way, it’s like opening the gate — the kids rush down the slide!

When a kid reaches the bottom and splashes into an empty spot (an electron recombines with a hole), all that extra energy turns into a big, colorful splash of light — that’s the glow we see from the LED!

Flip the battery? The gate stays closed — no sliding, no splash, no light.

Using different materials produces different energy responses. A taller waterslide makes a bigger, bluer splash; a shorter one makes a smaller, redder splash!