I don't see any light bouncing back at the ceiling, so I assume your problem is caused by a leak. These are caused when VVIS, a program critical to optimization and lighting, cannot run because it is unsure where your map is separated from an area outside of your map known as the void. To fix it, you'll need to review your compile log. If it has several errors and the text "*** LEAKED ***" at the end of your VBSP, you have a leak. Assuming you do have a leak, you'll need to load your map's pointfile. Under the map menu, an option should say "Load Pointfile". Clicking that should automatically load a pointfile, or ask you to specify a file if you have no leak in your map. Once loaded, you should see a red line somewhere in your level (usually coming out of the center of an entity.) Follow that line and it should manage to escape your geometry. You want to fix it so that it can't leave no matter what path it takes.
Keep in mind that leaks aren't sealed by glass, displacements, brushes tied to entities (including func_detail), or props, only actual brushwork!