The technology is there. There is an aquarist and he is a marine biologist in my town that is running coral fishtanks strictly with them(corals use photosynthesis just like plants do), he built them from scratch and he is beginning to market them and they are very expensive. The cheapest one he built he put 1000 bucks into for a 35 gallon tank. LEDs are coming, but it will be several years before they are affordable. But nothing out there says a weed wont grow under them now, but the outcome will probably be less than desirable.