I can't reproduce this.

Are those screens you are using all external screens or is one of them a laptop screen, and does the problem occur on all of them?

Does the issue persist if you disable automatically locking the screen in screen locking system settings?

Yes the screens are all external screens with one of them being a TV(which doesnt dim at all) 
The issue stops if I cancel the dim screen option in the Energy saving, didnt try to disable locking 

Also I am using x11 and not wayland

(In reply to xmakerenx from comment #0)
> SUMMARY
> After updating to Plasma 5.27.9 I noticed my screens will dims themselves to
> 30% brightness but won't un-dim after unlocking back from the lock screen
> My current setting in the Energy saving are 
> * Dim screen enabled with 5 mins 
> * Screen Energy saving with 10 mins
> 
> Issue seems to only happen after the screens were shut off
> In addition I use ArchLinux I have 3 screens setup but the third screen is a
> TV that is off most of the time and it seemed to happen regardless if the TV
> is on or off and I use an AMD GPU.
> 
> STEPS TO REPRODUCE
> 1. Enable the Dim screen with 5 mins and the Screen Energy saving options
> with 10 mins in the Energy saving settings
> 2. Wait for 10 mins until the screens will shut off
> 3. Move the mouse so the screens will be turned on again and see that the
> screen brightness was kept at 30% (dimmed) and not restored to 100%
> 
> OBSERVED RESULT
> Screens were kept at the dimmed brightness (30%)
> 
> EXPECTED RESULT
> Screens to be restored to normal brightness (100%)
> 
> SOFTWARE/OS VERSIONS
> Linux/KDE Plasma: Arch Linux
> (available in About System)
> KDE Plasma Version:  5.27.9
> KDE Frameworks Version:  5.111.0
> Qt Version:  5.15.11
> Kernel: 6.5.9-arch2-1 (64 bit)
> ADDITIONAL INFORMATION
> GPU : AMD Radeon RX 6650 XT

I've had this occur as well on an amdgpu as well, I have been digging to try to see if I can find anything in logs to explain this behavior. I did notice they dimmed after not using for a bit, and moved my mouse and it fixed the issue at that time, but if I wait longer than about a minute or two of them being dimmed, then they will not get bright again.

I can confirm this behavior myself.  Affected since pre-beta Arch build, continues to be an issue in 5.90.0-2 beta.  Also using AMDGPU.

also using amdgpu and similar issues here. I have been trying to investigate what causes it and now that I am on KDE 6 I atleast have a brightness slider to fix it after I log back in

Same here, AMDGPU and archlinux, plasma 5.27.10 . When the screen goes to sleep or after a while dims to 30% and have to move the slider to restore the brightness

The same happens on my PC, from time to time the screens will not return to 70% brightness, but will stay at 10-20%. Seems like it's happening only sometimes, not every time the screen dims. Everything was working ok before the recent update to Plasma 6.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: EndeavourOS
KDE Plasma Version:  6.0.1
KDE Frameworks Version:  6.0.0
Qt Version:  6.6.2
Kernel: 6.7.9-arch1-1 (64 bit)
Graphics Platform: X11

ADDITIONAL INFORMATION
GPU : NVIDIA RTX 3060 Ti

It seems that the issue stopped happening for me but not sure what changed that caused the issue to stop , I am currently on KDE Plasma Version 6.0.2.

Thanks, let's close this since you're the reporter of the original issue.

If other people can still reproduce the issue, it may in fact be a different issue, or have different root causes (e.g. different GPUs) so I'd recommend opening a new bug report about it. Thanks everyone!

*** Bug 488171 has been marked as a duplicate of this bug. ***

Re-opening since there are also new reports that look like the same issue.

Would you guys agree that Bug 452492 looks like the same issue? Also note 482713 that has a proof of concept patch for testing if a longer wait before the brightness write command can help.

Looks/sounds like it.

(In reply to Jakob Petsovits from comment #12)
> Would you guys agree that Bug 452492 looks like the same issue? Also note
> 482713 that has a proof of concept patch for testing if a longer wait before
> the brightness write command can help.

I am going to say possibly, however in this issue the reporter notes it can be fixed with brightness keys or running ddcutil in the console could fix it, in my situation, after this happens, nothing seems to fix it aside from a reboot. That command does nothing and sliders do nothing in the UI for me. After a reboot, I am able to use ddcutil and sliders in kde settings and everything behaves as expected. My work around has been to disable automatic dimming.

Hi all, I'm going to mark this as a duplicate of Bug 452492, which in turn I marked as fixed given the dimming rework that landed for the upcoming Plasma 6.3 release.

Relevant bugs that are still open at this point:

Bug 482278 (Screen remains dimmed after unlocking) - had some weird behavior where brightness would change not after waking up the monitor, but after unlocking the screen with a password when the screen had already been turned on. Waiting for the reporter to retest on Plasma 6.3 at a later time.

Bug 482713 (DDC-based Screen brightness control randomly unavailable in some sessions) - in a nutshell, if the interaction between PowerDevil and ddcutil fails, then everything else brightness-related also won't work, including restoration of un-dimmed brightness but also brightness applet sliders.

Please check if your issues are fixed with Plasma 6.3 once it releases. If you're still experiencing issues and feel like neither of the above bugs apply to you, feel free to speak out here or open a new issue with the particular behavior and setup of your system. Thanks!

*** This bug has been marked as a duplicate of bug 452492 ***