There are 3 ways to change screen brightness on Huawei Ascend P6 or most of the other Android devices. One from the notification panel, one from the menus, or let the device change the brightness automatically.
To change screen brightness on Huawei Ascend P6, do one of the followings:
1. Drag down the notification bar, and tap the Brightness button to toggle between: Minimum, 50% brightness, Maximum, and Automatic.
If Brightness button is not available, read How to Customize Notification Panel on Ascend P6 to add the brightness to your notification panel.
2. Open Settings and on General tab, open Brightness, and either manually change the brightness or mark the "Automatic Brightness" to set it automatically.