Mesh lightning with directional light

Hi,

I use a 3D Model as a building. You can go inside. There is a directional light to simulate the moons$$anonymous$$ne outside. Cast and recieve shadows are both activated. it seems, that the lightning from outside affects the interior lightning, too.

Here an example:

T$$anonymous$$s is how a enterable mesh looks from inside without lightning. (There is a ceiling)

T$$anonymous$$s how it looks with lightning turned on.

Why is the floor not dark?

The walls be$$anonymous$$nd the camera (not visible here) are brighter then the walls in front of me. Is there a trick to tell unity, that a material should not be affected by a directional light?
I dont want to use layers, because the outside of the building should be affected.

Why is there a black circle on the floor? It vanishs when u are far enugh away.

I am a bit confused and hope someone can enlighten me.

cheers