(Abbr. MH) A type of high intensity discharge lamp in which the major portion of the light is produced by radiation of metal halide and mercury vapors in the arc tube. Includes clear and phosphor-coated lamps that differ in their color-rendering characteristics.
Metal halide lights are a type of light bulb which burns very white and very bright. They require a special fixture and ballast. They are the closest thing we have to artificial sunlight, and are typically used on reefs and planted tanks. They are very efficient in terms of lumens/watt. Do not confuse these with halogen bulbs, which have a very yellow light not appropriate for aquarium use.
A type of projector lamp giving out a bright, clear white light, and used in many medium and all high-end portable projectors. These lamps emit a very high amount of light for the amount of power they consume. Unlike many other types of lamp, they slowly lose intensity (brightness) as they are used. These lamps output a very "hot" temperature light, Their whites are "extremely" white and make Halogen lamps whites look yellowish in comparison.