First thing, welcome to Tropical Fish Keeping forum. Nice to have you with us.
On the light. I will assume this is a T8 fixture, meaning that it takes the standard fluorescent tubes. "T" refers to the diameter in 8ths of an inch, so a T8 is 8/8 or 1 inch diameter. The older tubes that are being phased out were T12 so wider diameter. T8's are made in wattages specific to the tube length; some manufacturers make more energy-efficient tubes that have a slightly lower wattage with the same intensity, but otherwise all 18-inch tubes will be the standard wattage [not sure what it is, doesn't matter].
The T5 tubes that are becoming more common now require different fixtures; they will not fit the T8 fixtures, and vice versa. T5 are even more energy-efficient, and produce considerable light intensity. Anyway, these will require a new fixture [more in a moment on this].
Watts is somewhat meaningless as a guide to suitable lighting due to the vary different intensity from different tubes. Watts is only the measure of the amount of energy [= electricity] needed to light the tube. The phosphors and way the tube is made determine the spectrum and intensity, and both these aspects are critical when it comes to plants. I had a 55g with a single 40w 48-inch T12 tube years ago, back when these "Grolux" tubes were the thing for planted tanks. That was not intense light, but I did manage. Today with the newer T8 tubes a single 48-inch is suitable, or a single T5, but either means a new fixture.
Keeping the fixture you have, you would be best with the Hagen Life-Glo tubes; this is ideal light for planted tanks, high in the red and blue but with green to balance for a true rendition of fish and plant colours. The tubes that came with the hood are probably next to useless; my Aqueon hood was. I won't go into all that, but the Life-Glo would be better if you stay with the fixture. Low light and most moderate light plants should manage.
A better choice if you can would be a new fixture. As this won't fit the hood, presuming it is made for the tank, it would mean discarding the hood and getting a glass cover and a light fixture. The glass cover sits down on the lip around the frame, and the light fixture sits on the frame lengthwise. Before i go into the options for this, I'll wait for your response as I don't want to blab on without purpose.