I have an iMac/retina running High Sierra. When I bought it last year, I sadly learned Apple stopped creating Thunderbolt display and Cinema display, and instead recommended some 3rd party monitors (the two 4K Dell monitors I got among them).

Unfortunately, Apple doesn't seem to have addressed the problem of controlling their brightness through the keyboard, and that's much-needed functionality - to be able to dim them all together via the brightness key. That used to work, with my Thunderbolt display and previous iMac. So is a major problem, because adjusting display brightness in unison is expected, needed often used functionality. So it looks like we lost more than the Apple monitors/look-and-feel. We lost some essential integration.

Changing the brightness of the Dell monitors through their physical menu button on each of the two each time I change my iMac display brightness is extremely tedious and annoying. It involves several steps to reach the brightness adjustment interface.

I've looked for apps that resolve this, but there is not much out there that does it. I found one app on the Apple App store that works it by inserting an opacity changeable layer. It's sort of works but it's not implemented properly becauseit ruins screen capture - The layer they insert to darken the machines gets captured with the screen captured. I've found other flakey and unreliable apps too that work more organically, but they keep exiting so are not running when I need to change the brightness and I need to relaunch.

  • I have this problem too. Would be great if there was a way to control the brightness on dell monitor using the brightness keys (F1/F2) on the keyboard. – gprasant May 16 '18 at 16:48
  • I've posted an answer. It's not exactly what you want or think you need, but compared to the other 'solutions' out there, this is not bad once you get used to it, and I've explained how to make it viable. – clearlight May 17 '18 at 3:20

Update: The best solution I've found for this:

(1) Install XCode and all its developer tools/command line tools. (2) Install Brightness Menulet APP (3) Build the Brightness Menulet app in XCode (4) Install it into Applications.

You can have it launch at start. It's not rock solid and not under development. In particular it exits frequently if you have the mode set to automatically synchronize the brightness of your external monitors to the main monitor.

However, this is not the end of the world.

You can use CTRL+SPACEBAR and search for Brightness Menulet (and subsequent searches autocomplete quickly) to re-launch.

Although you can have the monitors automatically try to match the iMac main screen brightness, and it works, it will probably exit on you.

I find it plenty convenient enough to just individually set the monitor brightnesses via the apps menu bar drop down, since it isn't something I do often. It's just a LOT easier than having to do it manually via the hardware buttons/menus on the monitors!!

Hopefully someone will find time to fix it. I've considered it, but it works well enough for me so it isn't a high priority (and no I didn't write it and have nothing to do with the project).


I've found Lunar.app and it syncs the brightness from your PC to the external monitors. It has a lot of other features that I not yet have played with, but a uniform brightness is already great. The app looks nice, so thats a plus (and it's free).

Here is an article on lifehacker.com, because the information on the Lunar site is really sparse.

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