Two versions of a room exist - light and dark. The geometries of these two environments are similar, but slightly off. You live in one world. Using the flashlight, you can temporarily bring parts of the other world into existance, altering the geometry in front of you.
Concept
This video below is a simple concept that was created in the Irrlicht Game Engine.
Problems
How should physics work? What happens if the player is inside an object that doesn't exist in the other world.