you may not get enough light through the glass for one. But for another, the glass can block out part of the spectrum, making lots of alga grow.
If you wanted to do it a really good way tho, there are these things that i think are called something like sun tubes...might be something else. But they're expensive and you have to cut a hole in your roof. Basically a little dome sits at the top of your roof, and it catches sunlight (and moonlight which is cool) and has mirrors or something that redirect the light down the tube (which is pretty wide btw) and into the tank/fuge. I cant remember the exact name, but that kinda gives you an idea of what they are. I've seen where a guy here in AZ where im' at used them for his main lighting and has great success w/them.
