Planted Tank Guru
Join Date: Sep 2006
Location: Northern California
To start a planted tank, are you aiming for low light, moderate, or high light plants?
If it's a low light tank, you're going to need 1.5-1.8WPG, moderate is from 1.8WPG-~2.1WPG, and high light is higher than that.
The 100W CF bulbs are actually 23-25 watts. The 100W is an incandescent equivalent while the "WPG" (watts per gallon) measure is in fluorescent wattages.
If it's a low light to moderate light tank, I'd try to have at least 2, preferably 3 screw in bulbs over the tank, evenly spaced out. Dose with Excel and you should be set.