Turn Adaptive Brightness On or Off in Windows 8

1. Click on the Battery icon on the right side of the taskbar and go to More Power Settings.

2. Click on Change plan settings (the first one if you are using the Balanced battery mode)

3. Go to Change Advanced Power Settings.

4. The Advanced Settings wizard opens. Depending on your device, make sure to select High Performance or whatever you think will be appropriate for your device

5. Now select the item Display and expand it. Then select Enable adaptive brightness and also expand it. You can then enable or disable adaptive brightness using the dropdown box: