If your tank came without lights, buy a fixture suited for your tank, and if you have an option, get the fixture with room for more bulbs (better to have more than less).
If your tank came without lights, buy a fixture suited for your tank, and if you have an option, get the fixture with room for more bulbs (better to have more than less). A 3- to 4-foot tank or larger will require two to four bulbs overhead, though you can get by with less if you choose to use only lower light and/or floating plants, which will linger near the surface. For smaller tanks, a single fluorescent tube will likely work well for a normal 2-foot tank or less, as they are more shallow.