They are high intensity discharge lamps in which the major portion of the light is produced from a mixture of a metallic vapour and the products of the dissociation of halides.
 

Compared to high pressure sodium (SON) lamps, Metal halide, MBI, lamps offer similar advantages, but have different characteristics. The efficacy of MBI lamps is comparable to that of SON lamps, and they are available over a wider range of power ratings, 50 to 2000 W. They have a cooler, whiter, colour appearance than SON lamps. They have better colour rendering properties than SON lamps, and will thus be used where high efficacy and good colour rendering properties are required. However, as MBI lamps age, they can be subject to changes in colour appearance. A disadvantage of MBI lamps, when compared to SON lamps, is that they have a shorter service life; this should be weighted against the advantages of better colour rendering.
 

Recently, the increasing popularity of freestanding and wall-mounted uplighters means that these lamps are now also being used in office installations, although it is advisable to check colour rendering characteristics of the lamps before fitting an entire installation. In general, only those with better colour rendering, sometimes designated “deluxe”, are suitable for office interiors. Some of these lamps may also be used for display applications. However, they have significant restrike times, making them unsuitable for use with some control systems.