Light leaking through mesh with moveable light

For our world we have a dynamic sun, so we need dynamic shadows to cover the terrain, but we also have interiors to several buildings and currently the light leaks through the mesh like so.

How can we fix this problem as its pretty integral to get it working correctly.

Take a look at our Wiki Lighting Troubleshooting and tips guide here: A new, community-hosted Unreal Engine Wiki - Announcements - Epic Developer Community Forums

Thank you!

Tim