If you painted the wall, and got a screen...You could use the wall in conjunction with presentations. I assume those will be done lights on at least 50%. There is white chalkboard paint as well. I'm a fan of chalkboard paint since I've seen what a friend's wife does in a day care. They have a twin projector set up. One that does the entire wall during the day. And one that does 110 at night. Anyway. I assume some presentations will be slides via viewpoint. A painted wall allows the presenter to circle things(of course erase) as they go along.Then if the wall is white, get a negative gain screen(.7 or .8) to dial down the projector even more in low power mode.I'm under the assumption the room is never going to be lit lower than 20%.