Open Radar

 
Summary:
First we thought the current behavior is a bug, but then we found that this is by design:
https://developer.apple.com/library/ios/qa/qa1751/_index.html and as discussed here https://devforums.apple.com/thread/139813

As I understand, the reason is that the user should not be surprised by non-user-initiated changes in display brightness.

In our case though, the exact opposite happens:
We have a multiplayer card game ( http://boldpokerapp.com ). When a player folds and is out of the game for the next several minutes, their devices screen should go black to indicate that to the other players. To conserve battery (and make the black darker to look better) we also want to turn the UIScreen brightness to 0. The user doesn’t even notice, as the screen is black anyway. And when they can continue in the game, we turn the brightness up again automatically. 

However, the user now does notice and is surprised, when they want to switch to a different app or just want quickly check their messages, as they now find their devices brightness turned down and we have no chance to fix that before they leave the app.

We’d really love to use the UIScreen brightness feature for this, which would greatly reduce battery usage and provide a much better user experience. But for that we need a way to reset to the original brightness before the user leaves our app.

Thanks for considering!

Notes:
Example project attached, which shows the screen brightness is not automatically reset when the user leaves the example app.