Set your quality settings to “epic” → under the quick settings 
+ is there a light in the level which points into the direction of the window? (e.g a directional light which points at the windows) - also make sure to rebuild your light
Set your quality settings to “epic” → under the quick settings + is there a light in the level which points into the direction of the window? (e.g a directional light which points at the windows) - also make sure to rebuild your light