Shopping for lights for your aquarium can be one of the fun parts of getting everything set up just so. The fish don't need lights, unless they're kept in a room that's dark all the time, but you want to be able to see them, and show them off to your friends, don't you? Finding the right light can really unify your tank, make your plants and tank furniture look their best, and of course, show off the true beauty of your fish. For simplicity, we'll just talk about fish-only tanks here - planted tanks have their own lighting necessities. Lights for aquariums, like for every other purpose, come in two main varieties (with a couple of rarer and more expensive variants). Incandescent lights work like your standard light bulb. It costs less to buy them up front, but it takes more electricity to run them over time, and you'll also have to replace them more often.
In addition, they heat up your tank, which may require adjustments to your pH balance and will definitely promote the growth of algae. So, as you've probably guessed, I don't use incandescent lights for my aquarium. What I use, and recommend to you, is fluorescent lights. The bulbs and fixtures cost a little more than incandescents, but they are a lot cooler so they don't warm up your tank as much, and they make much better use of electricity, so they don't add to your electric bill as much.
Fluorescent bulbs also don't need to be replaced as often; maybe once every year to a year and a half, when the light starts to get dim. Here's a useful tip I got from my brother: spend a little more for a decent fixture that uses "electronic ballast" - it is inexpensive non-electronic ballast that causes the annoying "fish tank buzz" that most cheap fluorescent fixtures develop over time! It's worth the money if all you want to hear is the gentle bubbling of your pumps and filters. Now for the fun part - fluorescent bulbs come in a wide variety of colors.
Plain old white can be pretty harsh, and can make your tank look "washed out", so personally I tend to favor tinted bulbs. It may take some experimenting to find which colors show off your favorite fish to best effect, but in general warm colors like yellow or pink will make the tank look more vivid than cool colors like blue, green, or violet. Don't forget to buy a timer to turn the lights off automatically at night.
You should also be turning the lights off manually whenever you're not enjoying the tank - the more often the lights are on, the more they will promote the growth of algae in your tank.
Together with Iszuddin Ismail, Mic Hudson is sharing his wealth of knowledge on saltwater and freshwater tropical fish tanks. You can start with a free ebook on decorating your fish tanks. Download Fish Tank Aquascape at http://www.PetFishGuide.info