To change the brightness on an external monitor, use the buttons on it. You might not see the Change brightness for the built-in display slider on desktop PCs that have an external monitor. Even if you use it, you can still move the Change brightness for the built-in display slider to fine-tune the brightness level.

This automatic setting helps make sure your screen is readable wherever you go. Under Brightness and color, look for the Change brightness automatically when lighting changes check box, and then select it to use this feature. To find out if your PC supports this, select Settings > System > Display. Some PCs can let Windows automatically adjust screen brightness based on the current lighting conditions. (If the slider isn't there, see the Notes section below.) Select action center on the right side of the taskbar, and then move the Brightness slider to adjust the brightness. For more info, see Adaptive brightness and contrast in Windows. Some Windows PCs can automatically adjust the screen brightness and contrast based on content that’s displayed on your built-in screen. You might also see another check box displayed: Help improve battery by optimizing the content shown and brightness. Even if you use it, you can still move the Brightness slider to fine-tune the brightness level for a built-in display. Select Brightness, look for the Change brightness automatically when lighting changes check box, and then select it to use this feature.

To find out if your PC supports this, select Settings > System > Display. (If the slider isn't there, see the Notes section below.) Select the Network icon on the right side of the taskbar, and then move the Brightness slider to adjust the brightness.

Action center on windows 10