A fluorescent light is an electric lamp that produces ultraviolet light and converts it into visible light. The electric current used by fluorescent lamps is much less than that used by ordinary incandescent lamps to produce an equal amount of light. In offices and factories in the United States fluorescent lighting is the most widely used form of lighting.
How Fluorescent Lights Work
The most common type of fluorescent lamp is a long, sealed glass tube with a coating of fluorescent material on the inside. The tube has an electrode at each end, and it is filled with argon gas and a small amount of mercury vapor, at low pressure.
When alternating current is applied to the electrodes, they emit electrons. The electrons travel at great speed from one electrode to the other, creating a current through the tube. The direction in which the electrons travel is reversed with each alternation of the current.
On their way through the tube the electrons collide with atoms of argon gas, and additional electrons are set free. Many of the electrons moving through the tube strike atoms of the mercury vapor, giving them extra energy. As the atoms return to their normal energy states, they give off the extra energy as ultraviolet light, which is invisible. The ultraviolet light is absorbed by the fluorescent material, which then emits the energy of the ultraviolet light in the form of visible light.
Fluorescent lamps are classified as either cold cathode or hot cathode, according to the kind of electrode used. In hot-cathode lamps the electrodes are coiled tungsten filaments that are heated by a current of 1 to 2 amperes. Cold-cathode lamps have cylindrical electrodes that are coated with electron-emitting material. Cold-cathode lamps use less current and last longer than hot-cathode lamps.
Different fluorescent materials emit different frequencies of light. Each frequency corresponds to a particular color. By careful selection of the fluorescent materials to be used in the coating, it is possible to make lamps that produce light closely resembling daylight.
In 1867 the French scientist Alexandre Ed-mond Becquerel published a description of fluorescent lamps that he had made. He also produced designs for lamps that are very similar to those used today. Although their principles were fully understood, fluorescent lamps were not further developed until after 1920. Early fluorescent lamps required a high voltage and were used only in outdoor advertising signs. Low-voltage fluorescent lamps were first marketed commercially in the United States in 1938.