Metal halide lamps

In the last half of the 1960s, new high-intensity discharge light sources based on a halogen cycle have made considerable impact on the lighting market. Such light sources depend on the volatilization of halide compounds to introduce a variety of otherwise nonvolatile metals into a high-pressure arc in a fused silica tube. The excitation of these metal atoms in the arc then produces the characteristic spectrum of the metal; the incorporation of several different metals permits the generation of a number of wavelengths of light, i.e., substantially white light. These lamps combine the high output in a compact size of mercury lamps (to which they are similar in appearance) with the high efficiency and color qualities of cool white fluorescent lamps. Efficiencies as high as 100 Im/W are available in 1000-W lamps. Metal halide lamps are available from a number of manufacturers in this country and abroad and are finding wide application in industrial and commercial lighting, as well as in outdoor lighting installations where color quality is important.