Fluorescent Lamp, device that produces light by causing a substance called a phosphor to emit light, or fluoresce. Fluorescent lamps are cooler and more efficient than incandescent lamps, which produce light by heating a filament to high temperatures.
Fluorescent lamps use the fluorescing property of a class of materials called phosphors. When exposed to radiation such as ultraviolet light or an electron beam, phosphors emit visible light. Some examples of common phosphors that exhibit this property include zinc silicate and magnesium tungstate, the two materials most often used in fluorescent lamps.
A fluorescent lamp consists of a glass tube filled with a mixture of argon and mercury vapor and coated with phosphors on the inside surface. Each end of the tube is fitted with metal electrodes coated with a compound of an alkaline earth metal and oxygen, called an alkaline earth oxide, that produces electrons when connected to a power source. A device called a starter sends extra voltage to ionize, or give a net electric charge to, the gas in the tube. When current flows through the ionized gas between the electrodes, it emits ultraviolet radiation. The phosphor coating inside the tube absorbs this ultraviolet radiation and re-emits the energy as visible light.
Since the discovery of fluorescence in the 1600s, scientists have synthesized hundreds of thousands of phosphors. Each phosphor has a characteristic color of emission and duration of luminescence. Some phosphors, such as zinc sulfide and cadmium sulfide, are easily excited by a beam of electrons. As a result, these phosphors are used in the production of radar and television screens.
American engineer Peter Hewitt created the first mercury vapor lamp in 1901, which functions like a modern fluorescent lamp without the phosphor coating. The mercury vapor lamp emitted much of its radiation in the ultraviolet region of the electromagnetic spectrum. Engineers at General Electric Company were the first to combine phosphors with mercury vapor lamps to produce the first practical fluorescent lamp in 1934. Fluorescent lamps rapidly replaced incandescent lamps in industrial use and have also grown in popularity for home lighting.
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