Generating between 65 to 115 lumens of light per each watt of consumed electricity, metal halide grow light lamps are considered to have high efficiency. MH lights produce light, which is very close to the natural sunlight with the rich blue spectrum. Due to this, MH lamps support vegetative growing in the most desired way – when plants have many leaves on the stem with short internodes.
Structurally, metal halide lamp is a vacuum glass tube. There is also an arc tube inside, filled with mercury and other metals in iodine form. Under the influence of electric current, those metals start to generate light and heat intensively. Though metal halide bulbs can be either transparent or coated with phosphorus, the first type is more preferred for the indoor gardening, since it produces very bright light.
There are different sizes of metal halide lamps, starting from 70watts and finishing with 1500 watts. However 250w, 400w and 1000w are modifications, most commonly used in hydroponics systems gardening. In order to make MH light to work, it is necessary to use a ballast, designed for a particular bulb size. Ballast is, in fact, a transformer, which decreases voltage to some predefined amount.