Oh, DUH...would you look at that, 17 watts, right on there! : So I guess that makes my wpg a little less than 1. That should be fine for low-light plants, shouldn't it? Can you get bulbs the same length but higher wattage?
Are you sure it's a 24" bulb because mine is a 24" bulb and I have two and they are both 20w. A simple answer to your question, NO unless you change or make your own fixture. You can buy strip lights with compact fluescent bulbs or twin tube or get special lights that hang over your tank from special fixtures that are special for plants but they are expensive. Unless you want to spend a fair amount of money, probably 50$+ you can't change your lights. You can get reflectors to focus your light though.
It should say a higher wattage on the hood itself. What brand is it? From what I've seen the bulbs that come standard are fairly low-watt. I have a 32watt on my 55gallon and my Java Fern is growing ridiculously fast. Actually, it's more of a bush right now. I also have some swords and some floating plants which are doing quite well.