Light passing through static mesh, WHY?

Hi all,

I am working on a day night cycle and most of it works as intended. However, one issue keeps appearing, when the sun goes behind a static mesh a light glow will appear from the mesh (as shown in image). I do not know why this happens, can anyone shine some light on this issue please.

Note: Materials are set to double sided.

Larger Image Link; Screenshot - ff72a6f7fe3d0bac278102a66c6a7187 - Gyazo