Metal halide lamps are the type of lamps used to illuminate outdoor sports events because they emit a white light. Metal halide bulbs come in different spectrums – 2,100K, 3,200K, 6,400K, 7,200K, and 10,000K.
A metal halide bulb with a 6,400K, 7,200K or 10,000K rating is ideal for vegetative growth (18 hrs.) and for the first 2 weeks of flowering (12 hrs.). Using this bulb in early flowering will decrease stretching of the plant during the transition period from veg to bloom.
Using a 6400K, 7200K, or 10,000K bulb in the last 2 weeks of flowering will supply critical “UVB” light to the garden. Even plants grown under High Pressure Sodium lamps will have increased potency if the lamps are replaced with metal halide bulbs in the last 2 weeks of flowering.
Metal halide bulbs that are 2,100K and 3,200K are often the only bulb used during the whole life of the plant- vegetative and flowering stages. These bulbs have a mixture of blue, green, yellow, red, and orange spectrums which are sufficient for all phases of growth.
Metal halide bulbs come in 250w, 400w and 1000w sizes. These bulbs require a ballast to ignite them.
NOTE – It is unsafe to use a metal halide with a broken outer bulb. Not only does it emit large amounts of harmful UVB rays, it also releases UVC light, which is deadly to most life forms. DO NOT use a broken metal halide lamp.