brightness: Failed to set brightness of secondary display - Lenovo ThinkVision L2452p 24-inch

https://github.com/superduper/BrightnessMenulet and/or https://github.com/kfix/ddcctl may work for you. It sort of works for me with my current display, a LG 27MB85R (setting contrast works reliably; brightness and volume don’t, and querying volume hangs my Mac). See the caveats at the bottom of the ddcctl readme, though; it may also hang your Mac, display or both.

In any case, the above seems quite flaky and I don’t really want to release software that is likely to crash your Mac or display. If Apple decides to support DDC control in any serious manner I’ll reconsider of course.

Really disappointed at Apple; DDC/CI is so easy on Windows and Linux. Is there anywhere I can yell at Apple about it?

DP’s-iMac:~ root# brightness -l display 0: main, active, awake, online, external, ID 0x78c91d62 brightness: failed to get brightness of display 0x78c91d62 (error -536870201) display 1: active, awake, online, external, ID 0x78c91cf3 brightness: failed to get brightness of display 0x78c91cf3 (error -536870201)

I got sam error, and I am trying ddcctl and BrightnessMenulet, will update soon.

----- after tested ----- BrightnessMenulet is working for me, just download with the link https://github.com/superduper/BrightnessMenulet/raw/master/BrightnessMenulet/Brightness_Menulet.zip unzip, run the app, you will get it in top right corner, click and use it.

I am using 10.11.6 and have 2 ex-monitors it’s working.

Just created PR 49 to suggest the removal of hombrew from the README if there is no support for updating homebrew.

hi @latenitefilms if you download and compile the brightness code yourself it will work with you LG 5K UltraFine display

MY LG UltraFine 5K also fails when connected to my MacBook Pro via USB-C:

brightness -l
display 0: main, active, awake, online, external, ID 0x1b56fe4d
brightness: failed to get brightness of display 0x1b56fe4d (error -536870201)
display 1: active, awake, online, built-in, ID 0x4280c46
display 1: brightness 1.000000

However, I can use the brightness keyboard shortcuts to control the brightness of the external monitor, so macOS can definitely do it.

Also, as @jathu suggested, ddcctl also works.

I’ve got a Mac Mini with an M1 chip, MacOS 11.2.3, and an LG Ultrafine 5k Monitor. Using homebrew, I had a similar error in the issue description. I then downloaded the source, compiled it, put the binary in my path, and it works fine!

@nriley If you’d like me to provide further information, I’m happy to.

I have an LG UltraFine 27MD5KA and I get the same error:

$ brightness -v .9
brightness: failed to set brightness of display 0x1b561641 (error -536870201)