screen brightness changing

If the brightness changes even though the room lighting has not changed, the most likely causes are automatic brightness based on ambient light or content adaptive brightness control.

Try these in order:

1. Open Start > Settings > System > Display.
2. Under Brightness, turn off brightness automatically when lighting changes if that option appears.
3. In the same Brightness area, look for Change brightness based on content and set it to Off.
   • This feature can dim or brighten the screen depending on what is on the display, even when the brightness percentage looks unchanged.
   • Turning it off can reduce battery life.
4. If the device is a Surface, this behavior is normal for adaptive brightness and contrast. In Settings > System > Display > Brightness, set Change brightness based on content to Off.
5. If the brightness slider is missing or does not work, update the display driver:
   • Open Device Manager
   • Expand Display adapters
   • Right-click the display adapter
   • Select Update driver
6. If this is a desktop PC with an external monitor, Windows may not control brightness. Use the monitor’s physical buttons instead.

If the screen is changing every ~20 seconds, also check Start > Settings > System > Power & battery > Energy recommendations and see whether either of these is applied:

• Save power by screen contrast and brightness for the content shown
• Change brightness automatically when lighting around me changes

Those settings can cause repeated brightness adjustments.

• Change display brightness and color in Windows
• Adaptive brightness and contrast on Surface devices
• Learn more about energy recommendations