Ceramic metal halide (CMH) lamps combine high output with great colour rendering and good efficiency. They produce light by passing an electric arc through a mixture of gases. In a metal halide lamp, the compact arc tube contains a high-pressure mixture of argon, mercury, and a variety of metal halides.
Colour rendering is also important. This is the ability of a light source to show surface colours as they should be, usually in comparison to a tungsten or daylight source. Lamps with poor colour rendering will distort some colours.
One aspect of lamp colour is its colour appearance; whether the light from the lamps looks ‘warm’ or ‘cool’, measured by the correlated colour temperature (CCT). Lamps with a warm appearance having a CCT of 2700 – 3000K are generally considered appropriate in a domestic setting. Lamps of 4000K and above are considered ‘cool’ and are more appropriate for office and some retail applications.