Metal halide lamps have long been used by growers for the vegetative stages of growth. Metal halide can put out an intense blue light spectrum that works great with leafy greens like lettuce and herbs. Its because of this that many growers like to use metal halide lamps in the vegetative stages.
When using a metal halide lamp, an electrical ballast is absolutely needed to regulate the arc current and deliver proper voltage.
The lifespan of MH lamps can be as much as 20,000 more hours than a typical incandescent and are more efficient generating as much as 65-115 lumens more per watt.