Metal halide lamps are designed to mimic the amount of blue light that plants would usually get from the summer sun, and they are intended for use during the vegetative stages of the plant growth cycle.
The light output by metal halides is measured in Kelvins, with a higher Kelvin rating corresponding with a greater amount of plant usable light. These 600W metal halide grow lights from Sunmaster are rated 7200K (Kelvins) and are at the higher end of the scale, putting out plenty of that all-important plant usable blue spectrum light for optimum growth and performance.
Many professional growers use a mixture of metal halides and high pressure sodium lamps in their grow rooms, often using one 7200K metal halide for every two sodium lamps to add extra blue spectrum light to their environment. A set-up like this will often obtain great results, with plants having access to an abundance of usable light to ensure strong, healthy, vigorous growth.