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.