Problem with light
Any other relevant info? When/how did it start happening? What mod did you install to cause it etc? Is it 24/7 or only at night? Vehicle headlights affected also, or just streetlights?
Best guess, it's a 'visualsettings.dat' issue. Make a backup of your 'mods' folder 'visualsettings.dat' & then replace it with a vanilla one from the game folder to confirm.
If you don't have access to a vanilla 'visualsettings.dat' you can get one in this thread (post#9, bottom of page).