Able to produce high quantities of light very efficiently, metal halide lamps became commercially viable in the 1960s. While expensive and difficult to build, they produce approximately 75-100 lumens per watt, which is three-to-five-times greater efficiency than incandescent lamps.
Because they require high voltage to start, but then run on standard electric current, they require special fixtures with a starter ballast.
Metal halide lamps are used to light industrial buildings and sports stadiums as well as for street lighting.
They are characterized by an inner arc tube that contains gaseous mercury and compounds of metals with bromine or iodine inside of a larger, outer tube filled with argon gas with a slight vacuum.
