Pulse metal halide lamp

As one of the most efficient sources of high CRI white light, metal halides as of 2005 were the fastest growing segment of the lighting industry.[1] They are used for wide area overhead lighting[2] of commercial, industrial, and public spaces, such as parking lots, sports arenas, factories, and retail stores,[1] as well as residential security lighting and automotive headlamps (xenon headlights).

Metal-halide lamps are used both for general lighting purposes both indoors and outdoors, automotive and specialty applications. Because of their wide spectrum,[4] they are used for indoor growing applications, in athletic facilities and are quite popular with reef aquarists, who need a high intensity light source for their corals.

Metal-halide lamps are used in automobile headlights, where they are commonly known as "xenon headlamps" due to the use of xenon gas in the bulb instead of the argon typically used in other halide lamps. They produce a more intense light than incandescent headlights.

Another widespread use for such lamps is in photographic lighting and stage lighting fixtures, where they are commonly known as MSD lamps and are generally used in 150, 250, 400, 575 and 1,200 watt ratings, especially intelligent lighting.

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Like other gas-discharge lamps such as the very-similar mercury-vapor lamps, metal-halide lamps produce light by making an electric arc in a mixture of gases. In a metal-halide lamp, the compact arc tube contains a high-pressure mixture of argon or xenon, mercury, and a variety of metal halides, such as sodium iodide and scandium iodide, The particular mixture of halides influences the correlated color temperature and intensity (making the light bluer, or redder, for example). The argon gas in the lamp is easily ionized, which facilitates striking the arc across the two electrodes when voltage is first applied to the lamp. The heat generated by the arc then vaporizes the mercury and metal halides, which produce light as the temperature and pressure increases.
Common operating conditions inside the arc tube are 5–50 atm or more[6] (70–700 psi or 500–5000 kPa) and 1000–3000 °C.Like all other gas-discharge lamps, metal-halide lamps have negative resistance, and with the rare exception of self-ballasted lamps with a filament, require a ballast to provide proper starting and operating voltages and regulate the current flow in the lamp. About 24% of the energy used by metal-halide lamps produces light (an efficacy of 65–115 lm/W),making them substantially more efficient than incandescent bulbs, which typically have efficiencies in the range 2–4%.