I am using just under 2 wpg of light. I bought the light online; it is supposed to be "a great light for growing plants". To be honest, I can't remember what the name or anything is, as the light aspect of planted aquariums was extremely confusing to my math/science impaired brain!! lol.
I can tell you that although I think my light is "good" for my tank, my plants didn't really start taking off and growing and looking really nice until I started dosing flourish and excel. It also seemed that the taller they grew and got closer to the light, the better and faster they grow.