ultraviolet lamp

ultraviolet lamp, device that emits electromagnetic radiation in the wavelengths between those of visible light and X-rays. This radiation spans wavelengths from about 400 nanometers (1 nanometer is 10⁻⁹ meter), which corresponds to the visible-light region, to 10 nanometers, corresponding to the X-ray region. The sun’s rays are rich in such radiation, sometimes referred to as black light because it is not visible to the unaided eye.

Working principle

An ultraviolet lamp usually consists of an electric discharge lamp (a transparent container within which a gas is energized by an applied voltage) with a material that yields radiation at the desired wavelength. Ultraviolet lamps are usually housed in quartz or a special glass that transmits ultraviolet radiation more readily than ordinary glass.

Generally, the sealed quartz tube contains tungsten electrodes and a small amount of mercury vapor suspended in a noble gas (a gas that is not chemically reactive). An electric current is applied across the electrodes in the lamp, generating an electric field within the lamp. This electric field excites the mercury atoms, and these atoms enter a higher energy state. When the atoms return from the higher energy state to the ground state (the lowest energy level occupied by the atom), they emit ultraviolet radiation.

Applications

Ultraviolet lamps were developed for medical use after the germicidal qualities of ultraviolet light were discovered about 1900 by the Danish physician Niels Ryberg Finsen. Since then, they have been used for the sterilization of air in hospitals and laboratories, water purification, and disinfection in food processing and packaging. Modern lamps are also used in industry and research, in producing artificial suntans, and in creating special effects in lighting stages and displays with fluorescent materials.