Chosen Solution

When I switch on the screen is bright but after twenty seconds or so the screen goes dim.

Hi, You don’t state the model number of the tablet so hopefully the follow settings are also available in your particular Samsung tablet. Go to Settings > Display and Wallpaper and adjust the following settings to suit:

  1. Smart stay: Set the device to prevent the display backlight from turning off while you are looking at the display.
  2.  Screen timeout: Set the length of time the device waits before turning off the display’s

backlight. 3. Auto adjust screen tone: Set the device to save power by adjusting the brightness of the display

go to seting, display sleep after 5 minutes, you can change it any minutes you like