The ceramic discharge metal-halide (CDM) lamp, often referred to as Ceramic Metal Halide lamp (CMH) is a source of light that is a type of metal-halide lamp which is 10-20% more efficient than the traditional quartz metal halide and produces a superior color rendition of up to 96 CRI.
The ceramic metal halide is a variation of the metal-halide lamp which is itself a variation of the old (high-pressure) mercury-vapor lamp. A CMH uses ceramic instead of quartz like a traditional metal halide lamp. Ceramic arc tubes allow higher arc tube temperatures, which some manufacturers claim results in better efficacy, color rendering, and color stability.
The discharge is contained in a ceramic tube, usually made of sintered alumina, similar to what has been used in the high pressure sodium lamp. During operation, the temperature of this ceramic tube can exceed 1200 kelvins. The ceramic tube is filled with mercury, argon and metal-halide salts. Because of the high wall temperature, the metal halide salts are partly vaporized. Inside the hot plasma, these salts are dissociated into metallic atoms and iodine. The metallic atoms are the main source of light in these lamps, creating a bluish light that is close to daylight.