It depends on what you plan on keeping. Some species want low light, others intense... Generally you want about 3-5 watts per gallon unless the tank is abnormally tall, then you want even more light. Metal Halide is the "best", but it is expensive, hot, and you have to replace the bulbs often. If you are just wanting a regular tank without a bunch of corals, then power compact or t5 lights would work just fine and cost less.