Yes as long as your tank is not more than about 18 inches tall. You really (usually) want close to 5 watts per gallon. If you have an unusually tall tank, you will need more than that.
What you really need it the proper amount of light getting to the bottom of the tank. As tanks get taller, the water will absorb more light and not let as much penetrate. So if you have a tall tank, you will need more light than the recommended 5 watts per gallon.
What is it that you find confusing about lighting?