BSG put fake "shadow cubes" inside every interior to compensate for non-existing GI.
This mod gives you ability to tweak opacity of interior shadows.
In game press F12 and select mod to tweak settings.
Demonstration: https://www.youtube.com/watch?v=vhwed0I2r7E
Explanation: https://www.youtube.com/watch?v=jhVJkcdYPXU
