Metal Halide Aquarium lighting belongs primarily in the realm of commercial aquariums, marine aquariums, planted aquarium enthusiasts and those people with deep tanks.
In the real world metal halide lighting is often used in factories and warehouses because of their high light output and the fact that they are relatively small when compared to incandescent and fluorescent bulbs.
These lights require special light fixtures and normally range from 175 to 1000 Watts, meaning they are expensive to run. They also produce a lot of heat which has to be taken in account when positioning them.
Metal Halide lights are also available in a very wide variety of Kelvin ratings, from 3000K to 20000K. Due to factors in the manufacturing process the colour temperature may differ from bulb to bulb, but should only be by 100 to 200 degrees Kelvin.
In most situations metal halide lights are suspended over open aquariums instead of being mounted in a hood. This helps with keeping the heat down. Metal Halide bulbs give of a flickering effect and are often used together with fluorescent lighting to minimize this.
Some aquarists using this light in heavily planted aquariums are forced to use aquarium chillers to counteract the effect of the heat given off by the lights. Some light fixtures come with built-in fans to draw heat up and away from the water.
These lights really come into their own when being used in deep tank setups. The powerful light is able to be focused by the light fixture to penetrate deep into the water.
The chances are that this sort of extreme lighting will not be necessary for your aquarium, but if you are thinking of expanding to larger tanks then you may end up requiring some of these.
Specialists with planted aquariums look to replace these bulbs once a year to maintain proper lighting in their tanks.
These lights can be very bright. Care should be taken not to look directly into the light while it is switched on. There is a possibility you could cause damage to your eyes.