Metal Halide Bulbs
Metal Halide bulbs consist of an inner arc tube enclosed in a vacuum-sealed glass tube. Light is generated by passing an electric current through the inner arc, igniting mercury and other iodide metals inside the tube.
Advantages of Metal Halide Bulbs
Metal halide bulbs are a good choice for indoor gardeners because they are extremely efficient. The blue spectrum light they produce is quite close to the full sun in summertime. This type of light is best suited for plants in the vegetative growth phase.
Other Metal Halide Bulb Information
Metal Halide bulbs are available in many sizes, all the way from 70 to 1500 watts. The most common sizes are 250w, 400w and 1000w. You will also need a ballast matching the bulb size. The mounting position of a metal halide bulb depends on its type (usually marked on it somewhere). BU/BD bulbs are designed for vertical positions; HOR bulbs are horizontal; and U bulbs are universal and work in both positions, although they are usually more efficient when installed vertically.
Metal Halide bulbs should be replaced every 18 months to maintain top efficiency. If you're going to spend the time and money setting up an indoor gardening system, don't sabotage it by running weakened, outdated lights.