How to change an external monitor's brightness from your Mac

macOS only changes brightness natively on Apple displays. For most third-party monitors, Apple's own advice is to use the monitor's buttons and on-screen menu. The workaround is DDC/CI, a standard many monitors support for receiving brightness commands over the cable; apps such as MonitorControl and Slidr use it to control monitor brightness from your Mac.

What does macOS do on its own?

It depends on who made the display.

Apple's article on dark or low-resolution external displays says that if your keyboard and external display are made by Apple, the Brightness Up key works and System Settings, Displays has a brightness control. If the display isn't made by Apple, "you might need to use its built-in controls and menu system to adjust brightness".

There is one shortcut to try first. Apple's keyboard shortcuts page lists Control-Brightness Up and Control-Brightness Down to "change the brightness of your external display, if supported by your display". If that works with yours, you may not need anything else. For a lot of third-party monitors, it doesn't.

So with a non-Apple monitor you often end up pressing a small joystick behind the screen, which is fine twice a year and miserable twice a day.

What is DDC/CI, in plain English?

DDC/CI stands for Display Data Channel Command Interface. It's a VESA standard that lets a computer talk to a monitor through the same HDMI, DisplayPort or USB-C cable that carries the picture. Over that channel, the computer can set some of the monitor's own values. Brightness is the main one.

The useful bit: DDC changes the monitor's real backlight setting, the one in its on-screen menu. It isn't a dark filter drawn over the picture by the Mac.

macOS doesn't send these commands for third-party monitors itself. A third-party app has to.

Will DDC work with my monitor?

Often, but not always. A few things decide it:

The monitor comes first. Plenty of desktop monitors support DDC/CI, but not all. Some have it switched off in their menu, so if nothing happens, look through the monitor's settings for a "DDC/CI" option. The open-source MonitorControl project's README notes that TVs usually don't implement DDC, and that some displays (it names EIZO) use their own protocol.

Then the connection. The same README says DisplayLink docks and dongles don't allow DDC control on Macs, and that the built-in HDMI port on certain Macs doesn't pass it either: the 2018 Intel Mac mini, the M1-generation Macs it names (14 and 16-inch MacBook Pro, Mac mini, Mac Studio) and the entry-level M2 Mac mini. USB-C or DisplayPort directly to the Mac is the most reliable route.

Finally, the Mac. Apple Silicon and Intel Macs handle this differently under the hood. In practice that's the app's problem, not yours, but it's why one app might work where another doesn't.

Which apps can control monitor brightness?

Two worth knowing, described fairly (we make one of them):

MonitorControl is free and open source. It controls external display brightness and volume over DDC from your keyboard's brightness and volume keys and a menu bar slider. If you mainly want your keyboard keys to work on your monitor, start there. It isn't a trackpad tool.

Slidr is a trackpad app. It turns the left edge of your trackpad (built-in or Magic Trackpad) into a brightness slider, and with External Monitor Brightness turned on in its menu, that edge controls whichever display your cursor is on, over DDC. That setting is off by default, so switch it on after installing. The right edge does volume, and the top and bottom edges handle switching apps, keyboard backlight or media.

BetterTouchTool is the other name you'll see. It's a broad input customisation tool for people who like building their own gestures and shortcuts. The comparison page sets out how the three differ.

How do I set it up with Slidr?

1. Download Slidr from the download page and drag it to Applications. It needs macOS 12 or later.

2. Open it and allow Accessibility access in System Settings so it can read the trackpad.

3. Click the Slidr icon in the menu bar and turn on External Monitor Brightness.

4. Move the pointer onto the external monitor and slide one finger up or down the left edge of the trackpad.

Your MacBook's built-in display keeps using its normal brightness controls, and the left edge works for whichever screen the cursor is on. If nothing changes on the monitor, check its menu for a DDC/CI setting, then try a direct cable instead of a dock. The brightness guide has more on built-in displays.

Is there a free option?

Yes. If your monitor supports DDC, MonitorControl is free. Slidr is $4.99 once after a 3-day free trial, and it makes more sense if you want brightness, volume and the rest on the trackpad rather than the keyboard, especially in a Magic Trackpad desk setup. Either way, try the Control-Brightness shortcut first. It costs nothing to find out.