STALKER with the AMK mod runs very dark by default (or at least it did when I installed it) and the flashlight did basically nothing. I made some changes to the lighting settings as below. I don't remember what the defaults were when I installed, but as I recall, tone mapping (i.e. HDR) was switched off entirely which was the majority of the problem. There is already documentation out there on most of Stalker's console options, this just covers tone mapping specifically as some are undocumented and it took me a lot of playing with them to get good settings figured out.
In playing Half-Life 2 you may run into the problem that you get the message 'Node Graph Out Of Date. Rebuilding...' and from that point the AI may cease to function.