DGalt

So I'm trying to put together a new lighting system for my 15 gallon planted and am having a hell of a time doing it.

The housing for the fixture I can figure out, same with the reflectors (although, if anyone has any suggestions about making reflectors I'd appreciate that )

Florescent lighting, however, is just confusing. All I want is something that I can put 2x 15W T8 bulbs (these bulbs http://www.lightbulbsdirect.com/page...um/F15T8-AR-FS) in to. Really shouldn't be all that complex right?

My real question is what is the rule about putting different wattage bulbs into a florescent fixture. What I mean is, if a fixture is fitted with a 20W bulb, can you replace it with a 15W bulb (I was thinking of using two of these: http://www.amazon.com/LIGHTS-AMERICA.../dp/B00004WA4D)