This is the amount of light energy reaching an area, and while few light bulbs note the lumens, you can assume in the case of your standard fluorescent bulb that more watts mean more lumens.
There are two key components to aquarium lighting. The first is the output, measured in lumens. This is the amount of light energy reaching an area, and while few light bulbs note the lumens, you can assume in the case of your standard fluorescent bulb that more watts mean more lumens. Do note, though, that more efficient bulbs like compact fluorescent lights and T5s produce more lumens per watt than the older T12s and T8s, and LEDs are even more efficient.