A metal-halide lamp is an electrical lamp that produces light by an electric arc through a gaseous mixture of vaporized mercury and metal halides which are compounds of metals with bromine or iodine. It is a type of high-intensity discharge (HID) gas discharge lamp. The metal Halides improve the energy efficiency and color rendition of the light providing pure white light close to daylight frequencies. As a result, metal-halide lamps have high luminous efficacy of around 75–100 lumens per watt, which is about twice that of mercury vapor lights and 3 to 5 times that of incandescent lights and produce an intense white light. and are one of the most efficient sources of high CRI (color Rendering Index) white light.