How to lock the sun out of a room?

Well, basically assume I have an age with a sun, for the aboveground.
Then, I build a room (either above or below the plane, inside a mountain, does not matter); normally it would be darker in this room.
I know I can use the AMB slider to make the textures in this room appear darker - or other techniques - but my Avatar always draws shadows from the outer sun inside the room.
How can I get rid of this sun projected shadow?
It may be a simple or basic thing, but I didn't get even an idea when browsing the WIKIs.
Then, I build a room (either above or below the plane, inside a mountain, does not matter); normally it would be darker in this room.
I know I can use the AMB slider to make the textures in this room appear darker - or other techniques - but my Avatar always draws shadows from the outer sun inside the room.
How can I get rid of this sun projected shadow?
It may be a simple or basic thing, but I didn't get even an idea when browsing the WIKIs.