The brightness of the light did not change significantly or it would have caused the surroundings to get brighter, which they did not. For the same reason, that was not lightning. Lightning that close to the camera would have brightened the entire area drastically and likely washed out the entire video frame to a bright white for a short moment. At the very least, the entire scene would have been lit like daytime. That didn't happen. What you perceived as an increase in brightness of the lamp post was just the explosion's shockwave vibrating the shit out of the the camera optics or something.
