If you’re using Windows 7 or 8, and don’t have a Settings app, this option available in the Control Panel. 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.
This option is also available in the Windows Mobility Center. Right-click the Start button on Windows 10 and 8.1 and select “Mobility Center,” or press the Windows key + X on Windows 7. Change the “Display brightness” slider in the window that appears.
Information acquired from various helpful internet sources...