Depending upon your intention with respect to the type (species) of plants, the light you have can be sufficient. It is always best to have minimal than too much, and select plants accordingly. Algae will be less of an issue for one thing. But again, if your desire is to have a tank full of fast-growing stem plants, more light will likely be better. With what you have (using a good tube, more on this in a moment) your list of plants that will manage fine includes crypts, Anubias, Java Fern, Java Moss, most swords (the green leaf species), Corkscrew Vallisneria, Brazilian Pennywort (this is about the only stem plant I can think of that does OK in less light), and floating plants. My 33g is along this line, if you want to check the photos under "Aquariums" below my name on the left.
As for tubes, full spectrum or daylight are best. You can get the more expensive ones in fish stores (Life-Glo by Hagen, Ultra Sun by ZooMed, and Coralife makes one too) or check our hardware stores for "daylight" tubes with a kelvin of 6500K; GE, Phillips and Sylvania all make one.
Should you decide to upgrade the light, I would recommend a single-tube T5 fixture; this will take a HO tube and provide 1.5 times more intensity than the same length in T8. A dual tube fixture would likely be pushing the upper limit for a natural setup.