How to Control an External Display’s Brightness on macOS

To adjust an external display on a Mac, open Apple menu > System Settings > Displays, select the monitor, and move its Brightness slider if one is available. Some Apple displays and compatible third-party screens expose brightness to macOS. Many monitors do not. If there is no slider, use the monitor’s own buttons or a utility that sends brightness commands over DDC/CI.

Try the macOS brightness control

1. Connect and turn on the external display. Choose the Apple menu, open System Settings, then click Displays in the sidebar. Scroll if you do not see it.
2. Select the external display in the display layout or display list. If a Brightness slider appears, move it left or right and watch the external screen—not only your MacBook’s built-in display.

Apple documents brightness controls in Displays settings, while noting that the controls depend on the connected display. The brightness keys on a Mac keyboard may change the built-in screen without affecting a standard third-party monitor. If the slider is missing or does not change the external screen, move to the monitor’s own controls or the DDC/CI option below. See Apple’s Mac display brightness guide and external display setup guide.

Use the monitor’s built-in controls

Most monitors have buttons or a small joystick along the bottom edge or back. Press one to open the on-screen display (OSD), then look for Brightness, Picture, or a similar menu. Choose the brightness setting and raise or lower it. The button names and menu layout differ by manufacturer, so check the monitor manual if the controls are hard to find.

This changes the screen’s backlight or panel brightness at the monitor. It does not depend on macOS recognizing a brightness control. Apple likewise advises using a non-Apple display’s built-in controls when necessary. If you use an Apple display and its brightness slider is missing, check the cable and connection, then consult Apple’s external display troubleshooting steps.

Control a compatible monitor from the Mac

For a menu-bar slider or keyboard shortcuts, use a monitor utility that supports your display. One free option is MonitorControl. Its current project documentation says it uses DDC for supported external displays, Apple’s native protocol for Apple and built-in displays, and software dimming for some virtual or unsupported screens. DDC/CI is the monitor-to-computer control channel that lets software send settings such as brightness to the display. It adjusts actual monitor brightness only when the display and the entire cable or adapter path support that control.

1. Download the latest release from the official MonitorControl releases. Open the downloaded disk image, copy the app to Applications, and launch it.
2. Open your monitor’s OSD and enable DDC/CI if the option is present. It may appear under System, Setup, or External Control. The exact location varies by brand; some monitors enable it by default.
3. Click the MonitorControl menu-bar icon, select the external display if needed, and adjust its brightness slider. For keyboard control, open the app’s settings and choose the brightness keys or a custom shortcut. The project says macOS may request Accessibility permission when you use Apple’s native brightness or media keys; grant it only if you want that keyboard control.

With more than one monitor, check which screen is selected before changing brightness. MonitorControl supports per-display controls and also offers options to synchronize displays. For macOS 27, its README specifies version 4.4.0 or later. The project also notes that on macOS Tahoe, the system brightness overlay’s percentage may not update even when the control itself works; use the monitor or app slider to confirm the change.

If the brightness does not change

• Check the OSD first. Confirm the monitor’s own brightness can move. A locked picture mode or power-saving setting may limit adjustment; consult the display manual.
• Turn on DDC/CI. If a utility finds the monitor but the hardware does not respond, enable DDC/CI in its OSD, quit and reopen the app, then try again.
• Test the connection. Some docks, adapters, KVM switches, and DisplayLink connections do not pass DDC commands. If possible, connect the monitor directly to the Mac with USB-C or DisplayPort and test again.
• Know the software-dimming limit. If the monitor does not support DDC/CI, a utility may darken the image in software instead of lowering the backlight. That can reduce apparent brightness, but it is not the same hardware adjustment. Use the monitor’s controls for true backlight brightness.

macOS cannot add hardware brightness control to a monitor that does not expose a compatible control path. In that case, the monitor’s own buttons remain the reliable way to change its brightness.