Metal halide appears similar to incandescent lights but is more efficient in respect to intensities and wattage. Especially for aquariums we find metal halides in wide spectrum. This light has glass bulb with series of wires connected to the glass bulb inside it. The electricity passes through the inner glass bulb and produces light. Like the incandescent bulb the base is threaded but needs a special socket Mogul. The ballast needed by this bulb is placed below the aquarium.
The metal halide bulbs are very expensive and with the increase in the wattage the price increases. Either magnetic or electronic ballast can be used for this bulb. They have very high energy cost and they produce that much light which otherwise may require several bulbs to produce same amount of light.
But metal halide produces lot of heat and requires supportive system for the aquarium to combat heat. Moreover the bulb in operation is very hot to touch and could actually burst if splashed with water. It should be enclosed in a glass to prevent harmful UV radiation emitted by it to come out.
If you are planning to go for a very tall fish-only aquarium where high intensity light is required to illuminate the whole aquarium a metal halide system is to be used.
