This happens to me, too. Muzzle flashes and explosions are very weak in the night.
Whatever happened to the Muzzle flashes that were showcased in the videos that illuminated the environment so brightly? There's also a older screenshot of a muzzle flash here: http://media.pcgamer.com/files/2012/06/arma3_e3_201231.jpg

While it's on the screenshot not illuminating the environment, it's in a nightly setting and has full brightness and even a cool particle effect that we do not have in the Alpha. So since I don't know if Bohemia just changed their mind about them or if the current ones are just placeholders, I will support this ticket until we get a fix or if they are placeholder, until we get the real effects.