The Portico update for the Lumia 920 arrived only a few days ago with several new features, but it also brought with it a new bug. Some users are experiencing fluctuating brightness settings when their phone is set on auto-bright to the point that it becomes a severe battery drain. I myself noticed this while sitting on the couch playing a game of Wordament. The light from the lamp behind me was enough to cause the screen to go crazy trying to adjust. Thankfully, there’s a solution for this problem.
In order to fix the auto-brightness self adjusting too much, you’ll need to calibrate your phones sensors in the darkness. Head into your nearest closet, shut the door, and open up your settings to calibrate your phone. Then let us know if this worked for you. After completing the fix, I sat in the same spot and played the same game with no further issues.