This article was updated on the 11th September 2019.
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A fluorescent light bulb, such as those found in neon lights, uses an entirely different method to produce light than an incandescent light bulb. A fluorescent bulb is a gas-discharge tube which produces fluorescent light. There are a pair of electrodes at either end of a glass tube inside which small amounts of mercury together with an inert gas (usually argon) are kept under very low pressure.
When the fluorescent bulb is connected to an electrical circuit, the current flows from the circuit to the electrodes. There is a large voltage across the electrodes, which enables the current to flow. Similar to the stream of electrons in a cathode ray tube, a stream of electrons will travel from one end of the tube to the other end through the inert gas.
This energy causes some of the mercury particles suspended in the inert gas to transform from a liquid to a gaseous state. Some of the electrons and charged atoms moving through the tube crash into the mercury atoms, exciting them to higher energy levels. Ultraviolet photons are given off when the mercury atoms revert from their excited state to their initial, unexcited state.
Inside the glass tube is a coating of phosphor powder. Phosphor is a substance which emits light when it is exposed to light. The ultraviolet photons collide with the phosphor coating on the inside of the glass, which becomes excited with ultraviolet radiation and produces visible light.
An ordinary incandescent light bulb also produces ultraviolet light, but they cannot convert any of it to visible light. As a result, much of the energy used to power an incandescent light bulb is wasted. One major difference between a fluorescent and incandescent light bulb is that fluorescent bulbs convert invisible ultraviolet light to visible light, making them more efficient.
The other major difference is that an incandescent light bulb uses a lot of the energy it consumes to heat its metal filament and make it glow, whereas a fluorescent light bulb produces less heat. In general, a typical fluorescent light bulb is four to six times more energy-efficient than an incandescent lamp.