Metal halide (hid) lamps produce an intense bluish-white light, at a colour temperature of 5000-6500°k similar to sunlight, from an arc discharge between electrodes within a quartz capsule filled with special chemicals and are one of the most efficient ways of lighting large areas. The compact nature of the arc makes it easy to focus the light on a specific area. Plants grow well with compact growth under this light, but it lacks the red required for flowering. Lamps producing an enhanced orange-red output similar to a 3000°k source are available. Special starter circuits are required. Check that lamps will operate in a horizonal position if this is required.
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.
High pressure sodium lamps produce an intense pinkish-white light with a colour temperature of 2050°k from an arc discharge in high pressure sodium vapour and are an efficient way of lighting large areas. Succulent plants grow well under this light, but the colour cast may reduce acceptability for decorative illumination. The standard lamps are said to encourage production of flowers and fruit. Versions producing more blue light are available to promote compact vegetative growth, but this is not needed if the lamps are used to augment natural daylight which provides sufficient blue light.. Special starter circuits are required. Check that lamps will operate in a horizonal position if this is required
