To answer your last question Aquariumfishguy, the easiest way to get enough light to grow moderate light plants or less, is to have a second 20w flourescent tube in your canopy/hood. Unless you have a comparably deep tank in relation to it's length, you should be able to grow all but the high light plants with two flourescent bulbs over any tank. Notice that I said grow and not "thrive". Even in a 125 gallon tank, if you fit 4x3' bulbs over your tank (assuming 30 watts for a 3' bulb) you should have enough light to get by with low to moderate light plants. I say this to show that even though the watts per gallon rule would say this is relatively low light for this tank, a 125 gallon tank is a bit short for the amount of gallons it holds. A 6' 135 gallon tank would probably need at least 6 of these bulbs to perform similarly, due to it's added depth.
While this "2 bulb general rule" isn't flawless since many tanks have odd sizes, it will work for most setups provided you stick with Anubias, Java Fern, Java Moss, Crypts (some), etc. DO NOT attempt keeping high light plants and plants that get red/orange/pink colors.
I'm glad RTR cleared some things up for you about the wattages of incandescent vs. flourescent bulbs. Man, there seems to be more confusing help than beneficial help out there these days! I hope this helps out a bit.
