Under Windows this is what I use https://clickmonitorddc.bplaced.net to change such things.

Thank you! This works great! Another app for my list of portable tools.

Holy crap! This has been one of those things I've been wanting for so long!

Thanks!

This is great, thanks for sharing!

You are welcome. I just yesterday found about about this which updates most nVidia cards so that when the monitor in a multiple display setup are turned off all the windows on that screen do not get moved to the main screen.

https://www.nvidia.com/object/nv-uefi-update-x64.html

there's ddc, which has existed for a long time. It even worked back in VGA days. I automated some stuff with bash scripts and ddcutil on Linux.

Edit: DDC/CI to be precise, introduced in 1998: https://en.wikipedia.org/wiki/Display_Data_Channel#DDC/CI

It can be also exposed as kernel backlight device, then standard laptop GNOME/KDE brightness widgets just work.

How does one do this? On my desktop I currently use the ddccontrol and gddccontrol packages, but it would be awesome if the backlight slider existed the same as on my laptop.

There is simple driver: https://lore.kernel.org/patchwork/patch/753233/

As noted in discussion, Luminance VCD while worked for my monitors, backlight level 0x6B or legacy 0x13 would be better choice.

It then can be used by instantiating it at proper I²C monitor bus, e.g.:

    insmod ddcci_bl.ko
    modprobe i2c-dev
    echo ddcci_bl 0x37 > /sys/bus/i2c/devices/i2c-2/new_device

(oh, and it now over 2 years and I still haven't got time to integrate it with DRM display hotplug so it could be upstreamed :(

On Mac, I wrote a config [1] which uses `ddcctl` [2] cli tool to sync both brightness and volume using keyboard buttons. It worked quite well, although I haven’t used it for a while. I guess similar idea could be extended for linux too.

[1] https://github.com/prashnts/dotfiles/blob/master/etc/hammers...

[2] https://github.com/kfix/ddcctl/blob/master/README.md

Edit: Just noticed further down in the comments that an app exists for it now!

There's ddcutil for linux and this app for macOS

https://github.com/the0neyouseek/MonitorControl

My early-2000's Apple DVI displays support software brightness controls. Is that some proprietary feature that still hasn't been added to the general protocols?