Eli5; Why do halogen lights get burning hot but LEDS don’t get hot at all?
In: Technology
It’s about how efficient you can turn electricity to light. Halogen light bulbs work by heating up a filament inside. What’s different from regular light bulbs is that halogens ones can recycle the vapors of the tungsten filament inside – the filament gets “fixed.” However it works, it still works by making a metal very hot.
So, what about LED? LED uses electrons, or more specifically, photon emitting electrons, to produce light. How can it force electrons to only produce visible light (well, more than light bulbs, at least)? Well, here’s the answer.
There’s two semiconductors. When a current flows through it, electrons goes from one to another, releasing energy as photon during the process.
Now, why does it release electrons? So, semiconductors are usually made of silicon and another material (more in that later). Now, silicon has 4 electrons on its most outside shell. It bonds with each other using covalent bond, by sharing electrons and getting 8 electrons (the number of electrons that is most stable for that shell). Now, add an atom that has 5 electrons on its outer most shell. When it bonds with the silicon, you have 1 electron that is not used in the bond. Ok, we have a semiconductor that has 1 free electron (of course, it’s not only one but go with it). Next, we make the same conductor but this time the atom you add has only 3 electrons. Now, it needs 1 more electron to make 8 (the stable amount).
So, we have one semiconductor with a free electron and another semiconductor that needs 1 more. That free electron moves to the other semiconductor to fill the hole. Yeah, but why does it release a photon? Energy difference.
Only electrons with a certain energy level can be in a shell (well, orbital to be exact). Different shell have different energy levels. That means, if the electrons need to have an energy level of 1 to be in that shell, the electron needs to have an energy level of 1, not 1.1. The free electron has more energy than the hole requires. So what does it do? The electron releases energy, in the form of light. By the way, the energy difference between the semiconductors determine the color of the LED. If you want a blue LED, you’ll need a energy difference bigger than a red one.
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