Light bulbs used to be simple: just run a bunch of electrical
current through a thin wire until it heats up enough to start glowing. Bare
filament electric lamps were first demonstrated around 1800 by Humphry Davy,
and the glass bulb was added later to keep oxygen away from the wire so it
could glow for a long time without actually burning up.
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So the incandescent light bulb is 19th century technology, and by at the present there's now a blinding array of electric lamps - halogen light bulbs, fluorescents, mercury and sodium vapor lamps, LEDs, lasers and so on.
Each one makes its own clever use of physics to achieve the life goal
of a light bulb: converting electrical current into visible light. Here's how
they work.
Halogen bulbs have the similar tungsten metal filament as typical
incandescent light bulbs, but they contain a little bit of a halogen-based gas
in the bulb as well. The chemistry of the halogen gas allows it to capture
stray tungsten atoms that evaporate off the filament and shepherd them back to
where they belong, which both prolongs the life of the filament as well as
keeps the inside of the bulb clean and clear.
Fluorescent bulbs are basically gas-filled tubes with electrodes at
both ends – electrical current flows from one electrode to the other, and when
the electrons that make up the current bump into mercury atoms in the gas, the
energy of the collision makes the atoms get "excited" that's the
technical term and the atoms then emit visible and ultraviolet light.
The white coating on the inside of the flute absorbs the ultraviolet
light and re-emits it as more visible light - this process is called
"fluorescence" and is the namesake of the bulbs. For the reason that the
coating stops the UV light, it also keeps the bulbs from giving you cancer... except
that's what you want, in which case you can use a tanning bulb with a different
kind of coating.
Sodium, mercury, and metal-halide vapor lamps, which are commonly
used for lighting streets, warehouses, gymnasiums, and other large areas, are
also tubes that run electrical current through a gas. The gas itself emits
mainly visible light so these bulbs don't need a fluorescent coating.
Finally, LEDs are also like fluorescent light bulbs, except replace
the gas with a tiny crystal of semi conducting gallium, and throw away the bulb
so not like fluorescent bulbs.
But seriously, the semiconductor has two layers, one of which
provides excited electrons, even as the other provides a place for the
electrons to go and relax and that *is* the technical term. All you need is an
electrical current to transport electrons from the party side to the spa side
where they release the energy of their excitement as light. Voilá - alight emitting diode, perfect for human
parties!