Reference

The screen is dark.

    Make sure the screen brightness of your tablet device is not set at the lowest level.
    Make sure the remaining battery level is sufficient.
    Be careful not to cover the ambient light sensor.
    The screen may seem dark if used outdoors on a clear day.
    If you have the automatic brightness setting enabled, the brightness of the screen is adjusted automatically according to the surrounding brightness.
  • Tap [ Apps & Widgets] - [ Settings] - [Display] - [Brightness] - [Automatic brightness] to remove the check mark and disable the automatic brightness setting.