How do neon and fluorescent lights work?

Neon Light
Cool and colorful, eerily radiant, a neon tube emits a light of almost seductive elegance. But mesmerizing as their shimmer may be, neon system owe their glow to nothing more glamorous than a bit of gas and a jolt of electricity. Sealed within the glass tubing of, say, an illuminated signboard is a mixture of gases, one of which will always be neon. Left to itself, neon remains still and colorless. It is only when a current of electricity is passed through the gas that it reveals its garish talents.

When such an electrical change is applied, it stimulates electrons circling a neon atom’s nucleus. Though the suddenly excited electrons lack sufficient energy to elevate their orbits and move farther away from the nucleus. This condition lasts only an instant. Almost immediately, the electrons return to their unexcited state, emitting a burst of energy that is visible, as a brilliant orange-red application of a coating of phosphor powder to the inside of the tube will yield commensurate changes in color.

Common fluorescent lights found in homes and offices work on a very similar principle. Within the glass tube is not neon but argon and mercury vapor. An electric current introduced into the mixture makes the gases give off faint bluish light and invisible ultraviolet radiation. These emissions would be useless as a light source were it not, again, for a phosphor powder coating on the inside of the tube. This substance reacts with the wavelengths created by the gases and shifts them into the visible spectrum. So efficient is the process that a 40-watt fluorescent lamp can yield as much light as a 150-watt incandescent bulb. But it is not efficiency that makes these lighting systems so appealing. It is, instead, their endless range of hues – from soft room lighting to glinting crimsons – that earns such simple atomic reactions such universal attention.

Additional reading:
Neon lamp (Wikipedia)
Neon sign (Wikipedia)
Fluorescent lamp (Wikipedia)

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