I read an article somewhere that says not really. The biggest problem being that you cannot truly capture the sunlight. The sun moves all day long and therefore would be difficult to get a nice even light in the tank. You'd have to figure out where the sun sits the longest each day on your house and decide if that was enough. It might help to use one of those round bubble "quick lights" as the sun could be more easily picked up than with a flat piece of glass. I'll try to look around but I know it was in an article about MH and how to pick the right MH for your tank. I think the site was alink from coralreefbazaar but I don't have time to double check this morning.