I had a shop light with two 32w T8's on it (I'm thinking 40w bulbs are T12, but I could be wrong). I did pretty well with low light plants like java fern, anubias, and anacharis. The down side to having a shop light is that they waste a lot of light. Aquarium lights are designed to aim the light down in to the tank. Shop lights don't have reflectors exactly, and they're more for flooding a room full of light, so you'll see a lot of light going out the sides of the tank.
I agree though, if you get some good bulbs (between 6500k and 10,000k), you'll be able to pull off some low light plants fairly well. Just don't go dumping ferts in the water, you'll just be feeding algae.
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