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.
Outdoors on a clear day, you may feel the screen is dark.
If you have the automatic brightness setting enabled, the brightness of the screen is adjusted automatically
according to the surrounding brightness.
Tap [ Apps] - [ Settings] - [ Screen] - [Brightness] - [Automatic brightness] in that order to remove
the check mark.