Join Date: Sep 2003
Location: San Francisco, CA
Probably not if by "wide variety" you include high-light plants.
It depends also on the type of CF you're going to use. If you've got an eighteen watt twin tube, you might be okay if it's close enough to the tank's rim. (Even then, it'd be a stretch.) If it's a screw-in bulb, it won't be enough light for anything above mosses and ferns, I'd bet.
I believe that more important that wattage, is intensity (distance from the bulb to the plants) and spread (the effectiveness of the fixture's reflector).
In my tank of the same dimensions as yours, I'm using a twenty-eight watt screw-in bulb. While the intensity is fine for growing most anything, the spread of the fixture I'm using, a desk lamp, limits how well the plants are growing. At the same time, were I to put a twenty-seven watt twin tube on the same tank, it would be too much light given I'm not injecting CO2.
What type of fixture are you using? We can work from there.