Here's an article on how water lettuce grows indoors with good light.
http://aqualandpetsplus.com/Decor%20Dwarf%20Water%20Lettuce.htm
The leaf structure looks like water lettuce, but grows indoors like frogbit. Mine doesn't get huge in my pond, but it's still early - we'll see.
I've got scads of the stuff in anyone wants some for their pond (apologies if this should be in the classifieds instead).
I've discovered that the only thing worse than getting duckweed all over your arm is getting water lettuce all over your arm - yick.
I tried that last year. The water lettuce didn't grow at all in the pond. Plus any water lettuce that made it to the middle of the pond was eaten by the fish. Maybe someone eles will have better luck than i did.