I find Skyrim pretty much too luminouse , I barely can see the difference on a wall where is a lamp and the area not illuminated by it , most is very clear and visible , yes by night things turn more gray and less crisp but still you can see pretty much everything and very little light variations so much that sometime it is hard to guess where the light source is ...
the things that such e mod shoudl do to me is make the light contrast much more dramatic and evident , make dungeons dark and needy for light sources and torches , eventually even add more sources for light like carriable lanterns and more torches around to be buyed in emporiums...