Oh no, it's not a post-apocalypse story. It does take place during the process of the apocalypse. I wouldn't want to spoil the story too much, but basically that light was discovered rotating earth, as though it has a mind of its own. Countless monsters fell from the light, and anyone who stares into the light, or are exposed to it, for long periods of time, turn homicidal and some will slowly change into demonic like creatures.
The cataclysm and destruction, was the result of the military's failed attempt to wipe out all of these threats, using Kinetic Bombardment. The story will alternate through 5 different people's perspectives, and each one of their stories will unravel the mystery as to what the light is, where it came from, and why it's here.