Metal-halide Lamp

A metal-halide lamp is an electric light that produces light by an electric arc through a gaseous mixture of vaporized mercury and metal halides (compounds of metals with bromine or iodine). It is a type of high-intensity discharge (HID) gas discharge lamp. Developed in the 1960s, they are similar to mercury vapor lamps, but contain additional metal halide compounds in the arc tube, which improve the efficiency and color rendition of the light.

Metal-halide lamps have high luminous efficacy of around 75 - 100 lumens per watt, about twice the efficiency of mercury vapor lights and 3 to 5 times that of incandescent lights, moderately long bulb life (6,000 to 15,000 hours) and produce an intense white light. As one of the most efficient sources of high CRI white light, metal halides are the fastest growing segment of the lighting industry. They are used for wide area overhead lighting of commercial, industrial, and public spaces, such as parking lots, sports arenas, factories, and retail stores, as well as residential security lighting and automotive lighting.

The lamps consist of a small fused quartz or ceramic arc tube which contains the gases and the arc, enclosed inside a larger glass bulb which has a coating to filter out the ultraviolet light produced. Like other HID lamps, they operate under high pressure (4 to 20 atmospheres) and require special fixtures to operate safely, as well as an electrical ballast. They also require a warm-up period of several minutes to reach full light output, so they are not typically used for residential room lighting, which is turned off and on frequently.