Windows can adjust the brightness of the display depending on the amount of light that is reaching the computers ambient light sensor. This feature is referenced as adaptive brightness, and it can be disabled in Windows.

Press and hold the Windows key, and then press the q key.

In the Search box type, settings

In the search results list, touch, or click Settings (App).

Touch or click System.

In Display settings, select Brightness, then set the Help improve the battery by optimizing the content shown and brightness drop-down as needed:

Off: Adaptive brightness control is turned off and screen brightness, and contrast are not adjusted. This can result in shorter battery life.

On battery only: Adaptive brightness control is only activated when the device is on battery power.

Always: Adaptive brightness control is always running regardless of whether the device is plugged in or on battery.

Note: Some laptops do not support this feature, and the option is not available. You can manually adjust the brightness using the slider bar under Change brightness for the built-in display, and after making any wanted changes, close the System window. To check if the computer has an ambient light sensor, reference the computer manual.

Press and hold the Windows (

In the search box, type settings.

In the search results listed, touch, or click Settings (App).

Touch or click System.

On the display screen, ensure the box next to Change brightness automatically when lighting changes is cleared.
Now you can manually adjust the brightness by using the slider under Change the brightness for the built-in display.

NOTE: Some laptops do not support this feature, and the option is not available.

Close the Display window.