You can also try grading even if you did shoot in a dark area, using the gamma filter. Check the first video example on this page, marked 'muzzle flashes':http://fxhome.com/effectslab/
You can see the muzzles lighting up the actors and the ceiling in one clip particularly. It's simply a matter of using a grade object, masking the relevant areas and using filters to brighten up the area.
As hybrid says, the best way to get convincing lighting will be on-set lighting, perhaps using a controllable strobe of some sort.