Currently on my tank I have the single strip aquarium light reflector
that came with the tank. I have a 40w bulb (common enough item), and
so I average about 1 watt / gal.

What's the cheapest way to increase my lighting levels? Do they make
120 watt florescent bulbs? Or do I need to change the fixture itself?

Can anybody point me to some good DIY sites on this? And while I'm at
it, how bright should I go so that I can grow most hight light level
plants?

Thanks

Joseph