Since I have never kept animals that need UV, I just use fluorescent shop lights. My setup is a paludarium with a large terrestrial canopy build above a 55 gallon aquarium. I light the canopy from above with four 4-foot fluorescent tubes (in two shop fixtures). This serves the terrestrial plants and the plants growing on or near the surface of the water, but it doesn't penetrate very well down into the water. For that reason I have third shop light mounted behind the aquarium shining in through the back wall, which keeps plants on the bottom and in the water column nice and healthy. You might think that it looks kind of weird having lights behind the aquarium, but it works out pretty well. The back wall gets carpeted over with a nice layer of algae, and I have a herd of snails back there grazing.
This picture shows how the system looked a few months ago when I was starting a major rebuild, so the canopy is empty and the aquarium is neglected (but I think you'll agree I'd never have that much elodea growing down there without the backlighting). It looks a lot nicer now.
I was wondering about your duckweed (if that's what it is) because most plants that float on the water surface have pretty high light requirements (since in their natural habitat, open water, there isn't much to give them shade).
I like having duckweed on the surface, but I have two problems with it: I have to have it in a screened-off part of the surface or else it drifts to where my waterfall enters the aquarium and gets pulled under, and in the winter, when I bring in some outdoor goldfish for overwintering, they eat my duckweed.
Martin