Question: How does a LED light work, how can it give out light when you give it electricity?

Adrien Chauvet answered on 16 Nov 2020:

LEDs are the future of lighting.. because they are more energy efficient, more durable, cheaper, …

LEDs are made of semiconductor, which is a piece of (mixed) metal that does not conduct electricity so well.
If you force current (i.e. electrons) to pass through the semiconductor, some of the electrons will “fall” into holes; and as a result, they will emit light!

To give more technical details…
1. Semiconductors are made of metal atoms. These atoms are made of a nucleus and electrons. Most of these electrons are attached to their nucleus. We say that they are in the “valence band”. When an electron is not attached to a specific atom, they are considered to be free and they move freely in the “conduction band”. In terms of energy, electrons in the conduction band have more energy than one ones in the valence band.

2. Some semiconductors are lacking electrons due to some intentional defects. This results in “holes” in the valence band. They are called p-type semiconductors.

3. Now, if you pass current (i.e. free electrons) in a p-type semiconductor, some of these free electrons will “fall” into the holes.
By “falling” in the holes, these electron are going from the conduction band (high energy) to the valence band (low energy). They will then liberate some energy, under the form of radiation… i.e. light.

4. Different p-type semiconductors have different energy difference between their valence and conduction bands (called the “band-gap”). Hence, the free electrons falling into these holes can release more or less energy… which gives the different colours of light that can be emitted.

5. The larger the band-gap, the more energy is released, the more blue the light will be.
The smaller the band-gap, the less energy is released, the more red the light will be.

6. by superposing different types of semiconductors, you can even emit different colours at once… to generate white light!