Interiors Enhanced - Darker Ambient Light and Fog Mod
MODAmbient light power and fog brightness inside all interiors reduced by 60%, without touching any directional light sources whatsoever, keeping lighting 100% true to vanilla except for those dark corners and unlit areas.
Though not required, it is highly suggested to use this along with Darker Nights.
Incompatible with other mods that do the same exact thing, of course.