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mercury-vapor lamp[′mər·kyə·rē ¦vā·pər ‚lamp]
a gas-discharge light source in which an electric discharge in mercury vapor is accompanied by optical radiation in the ultraviolet, visible, and near-infrared regions of the spectrum. Mercury-vapor lamps are subdivided into low-pressure, high-pressure, and superhigh-pressure lamps according to the operating pressure. This pressure in turn depends on the temperature of the coldest section of the arc tube and the quantity of mercury introduced into the tube.
Low-pressure lamps, wherein the pressure is approximately 0.7 newton per square meter (N/m2), are efficient sources of resonance mercury radiation at wavelengths of 185 to 254 nanometers (nm). The most widely used lamps in this group are fluorescent lamps and bactericidal lamps.
High-pressure mercury-vapor lamps (104–106 N/m2) are efficient light sources that radiate predominantly in the ultraviolet and visible regions of the optical range. The spectra of these sources have a lined appearance with spectral lines in the wavelength range of 248 to 1,014 nm. The arc tubes of high-pressure lamps, which have a diameter of 8–60 mm and a length of 30–1,500 mm, are made of refractory, transparent quartz glass and are filled with an inert gas and a certain quantity of mercury. When the lamp is in operation, the mercury within the tube evaporates completely and creates the required pressure. The discharge is a bright arc that strikes across the electrodes along the axis of the tube. At pressures exceeding 105 N/m2, there appears a continuous background of radiation, whose intensity increases with the current density and pressure. The power ratings of high-pressure mercury-vapor lamps range from 50 watts (W) to 50 kilowatts (kW); their luminous efficiency is 40–60 lumens per watt (lu/W). High-pressure mercury lamps with outer bulbs coated on the inside with a phosphor are used for lighting. Lamps without a phosphor coating are utilized in medicine (phototherapy) and photochemistry and in photocopying apparatus.
Superhigh-pressure mercury-vapor lamps (above 106 N/m2) are sources of very bright radiation in the ultraviolet and visible regions. Their spectra have a lined appearance with the most intense lines corresponding to wavelengths of 312 to 579 nm. In both the ultraviolet and visible regions, a continuous radiation background is superimposed on the lined spectrum, and the intensity of the background increases with the current density and pressure. Superhigh-pressure lamps can have natural cooling or water cooling, according to which the arc tube will be, respectively, spherical or capillary. The power ratings of superhigh-pressure mercury-vapor lamps range from 100 W to 10 kW, and their luminous efficiency is 30–70 lu/W. These lamps are used in various optical apparatus.
Among the high-pressure and superhigh-pressure mercury-vapor lamps, the metallohalogen lamps are of particular interest. Here, the halides of certain metals are added to the arc tubes in order to increase significantly the efficiency and to vary within wide limits the spectral composition of the radiation.
Special starting and regulating devices must be used in connecting all mercury lamps to circuits.
REFERENCESRokhlin, G. N. Gazorazriadnye istochniki sveta. Moscow-Leningrad, 1966.
Rtutnye lampy vysokogo davleniia. Moscow, 1971. (Translated from English.)
G. N. ROKHLIN