This is a simple idea, not sure why it wasn't implimented to begin with! Glass walls or perhaps windows. They keep monsters from spawning inside your house, AND you can see the time of day in the background. Current 'windows' look ugly, and are just holes in the wall! Which is fine for some structures, but not all. Example, I'm building a potion growing/mushroom farm greenhouse and I don't want to fill it in with wall, glass wall would be perfect for this occasion. Looks nice, keeps the monsters out.