After updating to KDE Neon 6.2, the LED backlight brightness of my IPS monitor can no longer be adjusted with the brightness control slider.
Before the update, the slider would adjust the backlight of my monitor in the same way as ddcutil. For example, setting the slider to 0% would have the same effect as the command “ddcutil -d 1 setvcp 10 0”. Now, setting the slider to 0% just applies some sort of darkness filter over my screen making everything look low contrast and desaturated. The slider no longer has any effect on the backlight whatsoever. The ddcutil command is still working correctly. Enabling or disabling HDR has no effect.
Here is the output of kscreen-doctor if that helps:
Unfortunately, I have to reopen this again . Every few reboots, the issue reappears, seemingly random. I remember something similar happening in 6.1 as well, where sometimes the brightness slider just randomly disappeared, and I had to adjust the brightness with ddcutil instead. What else can I do to help identify the root cause?
I want to drop in and say that i have the same problem.
I change the brightness on my 3 monitors to 40%, after I wake them from standby they are back to 100% settings. All other settings are unaffected, its ONLY brightness.
restarting PC or waking from Standby does the same. It resets after the screen wakes up from Standby again.
quite annoying
I ended up replacing neon with tumbleweed. All problems gone. Brightness control working perfectly. Can recommend 10/10.
Just try tumbleweed live usb and see if it works for you as well
I tried using POWERDEVIL_NO_DDCUTIL=1
It didnt work unfortunately
its really strange though, cause i dont set my brightness on my KDE, i set it physically on the screens.
i NEVER had an issue like that, except since the update to KDE 6.2.
Something similar is happening on my Asus um325 laptop with kubuntu 24.10 and kde 6.1: After every reboot, brightness is at 100% no matter what it was set to before. But the slider shows the brightness setting I applied before last reboot. As soon as I move the slider even just 1%, the brightness is set correctly.
The weird thing is, the post/logo screen is set to the correct (pre-reboot) brightness while booting. If I go to bios before booting kubuntu it is also at the correct brightness. Which means kde does deliberately change it to 100% during boot
Not on Arch.
While with Plasma 6.2 my built-in Screen was as bright as I have never seen before, or maybe I imagine things.
I had some problem dialing it in fist.
Set the built-in to 30%, the next day it was back at 100% (even the slider), set it to 20% and after a reboot (reason Kernel update) every Monitor switched to 20%.
Edit: Have to correct myself, because I have just witnessed what sets all Monitor to 20%. That is really the mentioned powerdevil issue. But after reboot the (last) settings stayed. Edit-end
Apart that the brightness control does not work for one, of my two, external Monitor (and Kscreen-doctor says “Brightness control: supported”) it now finally seems to have settled in and keeps it different per screen settings, so far at least.
With Plasma 6.2.0, kscreen-doctor (via KWin/Wayland) claims brightness support for basically every screen right now. If PowerDevil exposes hardware brightness control for a given screen, KWin will use that. If not, or if the screen is in HDR mode, it will provide software brightness controls instead.
I have a patch in the works that would turn off the software brightness fallback if a display is known to support hardware brightness controls, but somehow lost them due to DDC/CI errors. So perhaps in future releases, brightness will not always be supported for a given screen. But the idea is that most screens should have something to adjust.
I have disabled the dimming for now, so (currently) no problem.
In the past (Plasma 5) I have tried but never managed to get DDC/CI brightness control to work with other Tools, because NVIDIA, technically Intel iGPU for most stuff except some Games but as far as i understand it is routed through the Nvidia card in my case. Therefor I was happily surprised enough that it now actually works with my main external one (the HDR one, probably the reasons).
I would call that a big improvement, even if it is not perfect (yet), nothing to be sorry about.
The other one can be set to HDR as well but because that caused issues with Plasma 6.0 at the same time my first try on Wayland, so heavy that it refused to boot (everything blacked out) and because that Monitor is literally secondary I decided HDR is not needed there and never tried again.
First of all, thank you so much for your work
I absolutely love the new brightness sliders, especially since KDE is the only desktop I know of that currently has this killer feature. All of the plug-ins/extensions/scripts I have tried over the years to simplify brightness control were annoying to install of have broken after a few updates. KDE having this by default is very practical, a true leap in user friendliness for external monitor brightness control
Software brightness control is awesome for systems without DDC CI or proper hardware brightness control. I have an old macbook lying around, and the only way to adjust its backlight brightness is installing an ancient proprietary nvidia driver which only works on top of an ancient kernel. Darkening the screen with software might not be quite as “” as native control, but since the latter is pretty much impossible without wasting a ton of time on a minor problem, it is nevertheless very much appreciated.
The root cause of the problem I described in my initial post may not be related to the plasma desktop or its dependencies at all. Since I switched from neon to tumbleweed a few days ago, the problem is entirely gone. Not only has the slider appeared after every reboot, it has also not even once failed to properly adjust the backlight brightness. This heavily implies that the root cause of the problem might be somewhere in the bug-ridden Neon distro and not the plasma desktop or its components. The problem seems like a single drop in the vast ocean of neon-specific bugs anyway, so I dont think it is really worth looking into as long as other much worse bugs are still present in neon.
The second “brightness resetting after each reboot” problem seems to be separate from the first one. In contrast to the first problem, I have experienced brightness resets on multiple distros and across different kde versions, but only on that one machine mentioned above (asus um325). The thread mentioned by @digitaltrails has multiple users with the same issue and on different hardware, so it might be worth investigating further. Maybe asking people for their hardware might help in determining the root cause.
. Every few reboots, the issue reappears, seemingly random. I remember something similar happening in 6.1 as well, where sometimes the brightness slider just randomly disappeared, and I had to adjust the brightness with ddcutil instead. What else can I do to help identify the root cause?
” as native control, but since the latter is pretty much impossible without wasting a ton of time on a minor problem, it is nevertheless very much appreciated.