No brightness slider on LG 5k Display Settings

I had a similar problem with a LG Ultrafine 4k and Macbook, connected via USB-C cable. I don't know if that's close enough to help.

Originally, the display settings had a brightness slider which worked. I was also able to control the brightness of the monitor by using the laptop keyboard, holding Control and the F1/F2 keys.

At some point, the slider was still there, but didn't do anything to the monitor's brightness. Also in this state, Control-F1/F2 showed the brightness overlay graphic on the monitor, but the display brightness did not change.

After some fiddling to get the slider or Control-F1/F2 to control the brightness, which included a reboot of the Macbook, the slider disappeared, along with the brightness overlay graphic.

A "Factory Reset" in LG Screen Manager didn't appear to do anything.

Also, when the slider disappeared from Preferences, the monitor's audio device disappeared in the Sound Preferences and menu bar volume.

Brightness control and audio device both came back when I reset NVRAM, having been inspired by this post: LG UltraFine 5K monitor - external devices not detected.

Monitor software version (3.11,3.4,5226,3.04,0.2f)

MacBook10,1 (Retina, 12-inch, 2017) 1.2 GHz Intel Core m3

macOS version 10.13.4 (17E199)

Now have the same issue. Originally was able to control the brightness via keyboard, but after a reboot all of a sudden have now lost the ability. No suggestions as of yet, but will try rebooting, etc.

Indeed, the same issue just developed for me: brightness control no longer appears in Displays for the LG monitor. Cold reboot of both the laptop and the monitor (LG Ultrafine 5k), to no avail. Made sure that the monitor firmware was up to date in the LG screen manager tool. Tried doing factory reset of the monitor, too.

Monitor version: 3.04,1.13,5237,3.04,0.1e.

I wonder if a recent update to either the screen or OS X broke something, but I don't think I had the screen auto-update.

As a temporary workaround, if you're experienced with developer tools, you can use this project on GitHub to manually control the brightness on the screen:

GitHub - unknownzerx/lguf-brightness: Adjust brightness for LG UltraFine 4K display (cross platform)

It's a little command line app you'll need to build from source and uses the reverse engineered protocol and libusb to control the display's brightness. I assume it was probably written as a start for getting support on Windows or Linux, but it works fine on MacOS.

The README is a bit sparse, but you'll need to install cmake and libusb from Homebrew, then run cmake followed by make to get a binary.

Obviously you can't use the nice apple brightness function keys like before, but it's at least something.

My brightness slider is finally back after it went missing in January. I'm not sure what brought it back, but I have reset the NVRAM recently for other reasons, so I'd say that is worth a try if you're having this problem. FYI, my audio device was working the entire time. I'm using a MacBook Pro 15" 2017 with the LG UltraFine 5K

see if the free software flux will do the job.

Thanks orospakr, this worked for me. I'd also like to note that the rotation control is missing too.

Same issue for me. Just happened over the weekend.

running Sierra 10.12.16