I don't think they're intentionally dark either (I watched someone's "Let's Play" video on Youtube and he didn't have any issues).

Specifically where you see a robot going into Beta on Level 2.

Turning gamma up does nothing (screenshot is with gamma whacked up full).

Interestingly if I apply a sight stim everything appears normal, but once that wears off, everything goes dark again and applying a second sight stim doesn't work - this is what made me think it's a bug rather than the area being deliberately dark.

I've tried messing around with resolutions, graphics settings etc. without success.

Has anybody else encountered this?

Beta entrance guarded by the bot is supposed to be dark. Look for a way into the engineering section of that floor - you will find four levers, one of them in a different position than the other three, Pull it and you restore power to beta

Ah, I totally missed that. Thanks Fenix!