This is a quote from Marijuana Horticulture the Indoor/Outdoor Medical Grower's Bible 2006, "Growers use HID lamps to replace sunlight indoors and grow outstanding cannabis. High intensity discharge lamps out-preform all other lamps in their lumens-per-watt efficiency, spectral balance, and brilliance. The spectrum and brilliance of HID's help growers replicate growth responses induced in cannabis by natural sunlight.
Watt for watt, a 600-watt HPS produces seven precent more light then the 1000-watt HPS. The pulse start metal halides are also brighter and more efficient than their predecessors. _