There are various kinds of tank lights available, but the type you need depends on what tank system you are running. For instance, fish only tanks can use a basic fluorescent light. When choosing a lamp make note of the "spectrum" of the lamp, which is the range of distribution of light. The rule of thumb for lighting is around 0.14W (1 Watt per gal) is a sufficient level to use.
Incandescent bulbs may provide many of the desired aspects of lighting needed by live plants. The least expensive fixtures are incandescent and take regular screw-in type light bulbs. The bulbs are also relatively inexpensive however, they need to be replaced much more often than other types of bulbs. Unfortunately, these bulbs put out a lot of heat, making it more difficult to regulate the temperature in your tank. Also these lights use more power for the light they give off than most other lighting, so you will have a higher power bill using this type of fixture.
While some types of metal halide bulbs produce desirable qualities of light at a low enough cost, they also drawbacks, namely that they are expensive to buy and generate too much ultraviolet radiation. If you do choose one of these units, make sure that it is designed for marine aquariums, and use an ultraviolet filter. Also be aware that these units get very hot and care needs to be taken to avoid getting burned.
Both metal halide and mercury vapor types of lighting share...read more