You’ll also see this option in the Windows Mobility Center. Open the Control Panel, select “Hardware and Sound,” and select “Power Options.” You’ll see a “Screen brightness” slider at the bottom of the Power Plans window. If you’re using Windows 7 or 8, and don’t have a Settings app, this option available in the Control Panel. Open the Settings app from your Start menu or Start screen, select “System,” and select “Display.” Click or tap and drag the “Adjust brightness level” slider to change the brightness level. You’ll find this option in the Settings app on Windows 10, too. On a touchscreen, you can also swipe in from the right side of your screen to open the Action Center. Click (or touch) and drag the slider to adjust your screen’s brightness. If you don’t see the slider, click the “Expand” option above the grid of tiles. To access it, click or tap the notification bubble icon that appears to the right of the clock on the taskbar.

On Windows 10, you can find a quick brightness slider in the Action Center.

Cannot adjust brightness windows 10