I would go with a new light fixture if you plan to get serious with planted tanks. A single bulb t5ho, dual t5no, or possibly a dual t5ho (a little overkill) are a good start. There are some cheap oddysea dual t5ho fixtures in 24" length on ebay. Do note that this may put you in the higher light range, though, so be prepared to start dosing ferts/co2
or raise the fxiture off the tank a little bit. You could also put a light diffuser across the top. IME it's easier to decrease light intensity than it is to increase it.