Near the end, the EMP (eletro-magentic pulse) device operates nothing like a real one would. The effect would be largely or entirely invisible, would not have a fixed radius but would dissipate slowly over distance, and it would cause all electrical systems with long enough lines to be overloaded and fail; even if the power stations were still supplying power in such an apocalypse, immediately after the EMP fires, none of the nearby lights-some of which are quite close-should be on. This is not required for the movie to work, either; the drones emit their own light, there is moonlight, etc. that would have allowed the action to be filmed still.