I found light to be my biggest enemy. Most of the upgrades available have something to do with your darkness powers, which are almost all disabled when you're exposed to light. Most of the time, however, I can see just well enough to fire accurately at foes, so if they shine a bunch of lights at me, I can still fire a shower of bullets from my SMGs or from my carbine if they're not close enough. Light almost never kills or incapacitates you directly, but mostly just limits your combat capabilities to whatever guns you have.