The funny behavior when you go outside is normal. When you first go from inside to outside during the day, it is really bright then mellows out. Or if at night it will be really dark, and then lighten up. I am pretty sure that is an intentional effect to simulate natural eye adjustment(or I could be giving them more credit than the dev's deserve on this one).
However, going pitch black by the sonar man, that is weird. Has anyone with the same card tried enabling some mods, especially one that changes the lights.cfg file? Try
http://www.filefront.com/15987937/Na...0Mod%20V1.0.7z
I have tested it with version 1.2 of the game, and it works fine. I know it does some other stuff that you may not want, but this would be the most likely mod fix for this problem.