In real time 3D game engines most areas are constructed with an ambient light that automatically lights all surfaces in the map uniformly to a specific level. This is done to ensure all details of the environment are visible in some way or another. The ambient lighting in most houses is very high meaning it doesn't matter how much you enclose a room you won't get it dark because the surfaces are being told to emit as if light is reflecting off of them, even if there is no light hitting them.

That said night fall crates come to crown store later this month. There is an fx tendrill item in them that will actually apply a shadow effect over a small room sized area. This can be used to significantly darken rooms.