So... Did you already pick up the lantern battery?
In the very beginning of the game you might need to get the generator key and turn on the generator behind each building (and hit the light switches in wach room) in order to see well.
After a while, you pick up a battery that allows you to iluminate the area in front of you at the click of a button. (B on the XBox controller, I don't know which button it is on keyboard and mouse. I think you need to open the item menu and use the battery before the lantern becomes available, tough.)
If you don't do that, then yeah, some areas will be pretty dark. ^^;