Fluorescent lamp, tube-shaped electric light from which light is emitted by the process of fluorescence. Fluorescent lamps produce about one-fifth the heat of light bulbs (incandescent lamps), use one-fifth the electricity, and lasts far longer. Fluorescent lamps, first introduced at the N.Y. World's Fair in 1938–39, are used largely in offices, schools, and factories. Inside a fluorescent lamp's glass tube is a small amount of mercury and a chemically inactive gas such as argon. The surface of the inside of the tube is coated with chemicals called phosphors. On each end of the tube is an electrode, which is a coated coil of tungsten wire. A ballast provides voltage to start the lamp and also regulates the flow of current. When a fluorescent lamp is turned on, electricity flows through the electrodes, heating it so that it gives off electrons. Some of these electrons hit the argon atoms and ionize them, giving them a positive or negative charge. Once ionized, the argon can conduct electricity. A current flowing through the gas from electrode to electrode forms a stream of electrons, exciting the electrons in the mercury. As the electrons in the mercury return to their normal state, they emit ultraviolet rays, which in turn cause the phosphors to glow (fluoresce).
See also: Fluorescence.