By default the lighting is sampled at the surface of the mesh to provide the most accurate lighting possible. This ensures that even very large meshes are always lit to match their surroundings.

Sampling lighting at the surface of the mesh can sometimes result in a light leak when the mesh is large and intersects a wall that separates a bright area from a dark area. To work around this type of light leak, you can force the sample location to the center of the component's bounding box. To do this, set Probe Sample Location to Bounds Center.