I can now control external display brightness from KDE and I don't know why. Thank you, nameless Linux contributor

submitted by edinbruh edited

This is a short appreciation/user experience story. Tl;Dr I'm enjoying my time on linux

I have been using Linux for a while (gnome for a year with an Intel UHD gpu, and KDE for a couple of months on a recent AMD gpu), and till now there was no brightness slider. Moreover, I have used the same display with windows for several years and there was no slider as well.

As far as I know (I looked up online some years ago, but this info is sometimes hard to find) my display supports DDC/CI but doesn't expose brightness (haven't actually tried).

For some reason, about a week ago a brightness slider appeared on KDE but it didn't do anything. Yesterday while updating some unrelated stuff I noticed the slider again and moved it for shit and giggles, and the brightness actually changed...

I have several questions... and I don't even know which piece of software is responsible for this... but thanks

I have been using Linux on and off for several years, often alongside windows, but I have entirely switched to it (almost, I still have a windows PC that I use once in a while) about 16 months ago. I have to say that Linux does take a lot more effort in getting some things to work, but when everything goes smoothly it's sooo good, and improves every month.

In the span of a year my desktop experience has only got better. But the shock was when I booted up an Ubuntu 16.04 cd I had lying around to fix grub on a dual boot machine and it was barely usable. Now instead it's almost "plug and play". Plus Nvidia cards are getting more and more usable with every update, explicit sync is almost merged, and prime works fine already.

There won't be a year of the Linux desktop anytime soon (there's still too much that needs improvement), but the next years will definitely be exciting.

P.s.: does any of you know why display brightness works now?

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I always see "this doesn't work, why?" posts, it's the first time I see a "this works, why?" post XD

edinbruh [OP]

I *am* a computer scientist after all


Flex that chaotic good!

refreeze , edited

Probably using ddcutil. There is a popular gnome extension for the same thing: https://extensions.gnome.org/extension/2645/brightness-control-using-ddcutil


Correct. It's a combo of powerdevil and ddcutil. https://invent.kde.org/plasma/powerdevil/-/blob/master/CMakeLists.txt#L67


I don't even know this is possible!


This has been a game changer for me With this and the toggle for light/dark mode I can adjust the brightness of my screen without using the clunky interface of my monitor


It works for me as well - Asus VG259Q. I'm surprised my screen even has this feature, and even more surprised you can do that over DisplayPort. Even Windows doesn't have that lol


It's a very common feature for monitors, at least in my experience - both of my cheap AOC monitors support it, as well as all the other monitors I've ever connected my laptop to (a few HP and Samsung monitors iirc).

But it also feels kinda janky due to how long the display takes to change the brightness, so maybe that's why Microsoft decided not to support it?


Hm, maybe it's an issue specific to your screen? On my end the brightness adjustment is instant


Maybe. To be clear the delay isn't that large (my very rough guesstimate is somewhere between 100 and 300 ms, probably more towards the lower end), and if I just click somewhere on the slider, it feels fine.

It only feels janky when I drag the slider and the screen brightness updates in very noticeable steps. But that is how I naturally interact with sliders, so it's hard not to notice it for me.


Oh, it's the same then, thought we were talking about delay in seconds x3


There wont be a year of the Linux desktop, it will be little increment in users over time. Plasma 6 is AWESOME.. I noticed this feature with kde 6 so i guess its backed into it

jlow (he/him)

So we are not talking about Plasma 6 but a random system update? What distro are you using? I have a "This is not working, why" story that I would love to get fixed magically: my laptop's brightness control stops working after the laptop sleeps for the first time after booting. No idea what to do about it, for the time being I use xrandr brightness under X ...

edinbruh [OP]

Not plasma 6, random fedora 39 update

jlow (he/him)

Interesting, thanks for the answer.

Kilgore Trout , edited

This is the commit that "magically" made it work: https://src.fedoraproject.org/rpms/powerdevil/c/7ce3c53429c16e84bf805299b86fcc313701b1e6

Your post may be more constructive if you specified your distro (Fedora 39)

DDC/CI has been (re-)supported by powerdevil since https://invent.kde.org/plasma/powerdevil/-/commit/e4a5e5d3e017ef45979933e14e47408bb3a59dda and included in release starting from Plasma 6.0.0

Quack Doc , edited

Most displays support DDC, the feature has actually been in powerdevil for a while, but disabled due to bugs.

EDIT: modern displays*


Is it actually changing your display brightness or is it just doing a visual overlay like flux?


Real, and will even do all monitors too if you have more than one. I have one that doesn't support DDC and brightness doesn't change.


I noticed this as well a few months ago and it did change the monitor brightness for real, but now it broke on my system and wont do it anymore


I can change my screens too on desktop, pretty neat.
Unfortunately its a super simple implementation which doesnt take into account the brightness between different screens.

Ideally there should be a master slider and one per screen. The master slider should then use theother sliders current value as scaling factor to change them.
A more complex option could then also allow setting the brightness of each screen which would allow for better setting via the master slider. (not sure if this information is already available)