: How does flowing electricity in a closed circuit lead to an LED lighting up?

Question

An LED (bulb) lights up when it is in a closed circuit with a battery. ‘Because electrons flow in the circuit’. But what is the mechanism that transforms this kinetic energy of electrons into light energy? Should I be asking a different question?

In: 32

Answer 1

Electrical circuits can be thought of like water circuits. Water inside a pipe with high pressure wants to get out of the pipe or move to somewhere with low pressure. The same is true of electricity. Electrical “pressure” is denoted as voltage, and electrons inside of wires with high voltage want to move their pressure/energy to somewhere with low voltage.

Batteries bestow voltage (electrical “pressure”) to the positive terminal of the circuit it’s attached to in the same way a pump bestows water pressure to the connection at its outlet. Now if you route that wire (“water pipe”) to some kind of machine or system you can make it do useful work using the higher voltage (“higher water pressure”) you’ve sent over.

So now let’s talk about our LED. The water analogy does break down a little but it’s mostly to set the stage in understanding voltage. We have our battery and some wire to send higher voltage (“higher pressure”) electrons to one side of the LED, and some return wire from the other side of the LED back to the negative side of our battery.

Most LEDs are made up of a special combination and arrangement of materials that allow only a very specific voltage change across it. It can be more – but more importantly – not less. This doesn’t stop our higher pressure electrons though. They are Stull pushed across this gap, forcing the electron to accommodate the minimum voltage change as it jumps. It loses this voltage all at once by emitting energy in the form of a light particle (photon). This is happening continuously with every electron pushed across that gap, resulting in the light we see.

By cleverly selecting the materials that make up this gap, we can dictate the electron voltage lost as it jumps across, which means the photons are released at different levels of energy, which appears as different colours.