In my experience it is a good idea to start a newly set up tank with fairly low light, for example, one to two watts of cool-white T-12 fluorescent per gallon. If the plants get off to a good start, one can cautiously increase the light level. If you prune back a major amount of the plants as I often do because, being busy or lazy, I let the tank get badly overrun, then it is a good idea to cut back on the light to reduce an inevitable algae bloom.
Most of my tanks are 15 or 20 gallons, and I make---well I wouldn't call them hoods---fluorescent light fixtures that sit on top of the glass covers on the tanks. I made some fixtures that hold three 20 watt T-12 lights. Each light has its own ballast, making it possible to have one, two, or all three lights on. This gives me lots of flexibility in getting the tank started up. When the plants are well established and algae is under control, I can replace the fixture with one that holds four, 24 inch, T-8 flouroscents, all run by a single ballast. If I want more light than that, I can put on a fixture that has two 40 watt compact fluorescents. I only use this last fixture on tanks that are very heavily planted.