Ambient light sensor readings got quite a bit of an overhaul in iOS 6, and now include Lock screen auto-brightness and better memory management. This has lead to many people experiencing issues with auto-brightness settings. iPhone 5 users in particular seem to be having trouble. If your auto-brightness isn't working under iOS 6, here's how to reset it and get it back in gear.

  1. Go into a dimly lit or dark room.
  2. Launch the Settings app from the Home screen of your iPhone, iPad, or iPod touch.
  3. Tap on Brightness & Wallpaper.
  4. Turn the auto-brightness setting to Off.
  5. Adjust the brightness slider to the level you would like your screen brightness to be at in the given environment. For instance, if you're in a completely dark room, you'll probably want to put the slider all the way to low or pretty close to all the way down.
  6. Turn the auto-brightness setting to On again.
  7. Now flip on a light switch.
  8. Watch the brightness slider move upwards to adjust to the new light entering the sensor.

As long as the brightness slider is moving on its own, you have successfully re-calibrated the sensor and it should work properly from here on out.