Bug 494815

Summary:	Display randomly has low brightness (one or both monitors)
Product:	[Plasma] plasmashell	Reporter:	Arnab Bose <hirak99>
Component:	Power management & brightness	Assignee:	Plasma Bugs List <plasma-bugs>
Status:	REPORTED ---
Severity:	normal	CC:	danipo, jpetso, natalie_clarius, nate, o.malek.cz, ollie, phil.hord
Priority:	NOR
Version:	6.2.4
Target Milestone:	1.0
Platform:	Gentoo Packages
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:

Description Arnab Bose 2024-10-15 13:36:35 UTC

SUMMARY
Often one or both of my monitors have very low brightness on session start.

STEPS TO REPRODUCE
0. Use Wayland.
1. Log in to a session from SDDM.
2. If monitors have normal brightness, log out and go to 1.

OBSERVED RESULT
One or both monitors have very low brightness.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.2.0
KDE Frameworks Version: 6.7.0
Qt Version: 6.8.0
Kernel Version: 6.11.3-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 16 × Intel® Core™ i9-9900K CPU @ 3.60GHz
Memory: 31.1 GiB of RAM
Graphics Processor: NVIDIA GeForce RTX 3090/PCIe/SSE2

Also, this is a desktop system with two monitors connected.

ADDITIONAL INFORMATION
1. Started once I updated to KDE 6.2.
2. I could not reproduce it on X, only happens on Wayland.
3. This is NOT likely related to ddcutil - the value it sets matches the value I see in monitor.

Unfortunately I have not found a way to correct the problem even after logging in, except to log out and log in again, or reboot, and hope for the best.

I am unsure if it is an issue with powerdevil, but brightness appears to be related to it?

Comment 1 Arnab Bose 2024-10-15 13:42:14 UTC

More info: 

Once logged in, enabling / disabling / disconnecting / reconnecting monitors don't appear to make a difference.

However logging out and logging in again appears to reroll the dice on whether brightness will be low this time.

Comment 2 Arnab Bose 2024-10-16 02:47:23 UTC

NVidia Version: nvidia-560.35.03-13

Comment 3 Ondrej Malek 2024-10-18 11:02:12 UTC

I have same issue + "Power Management -> Change screen brightness" does not have any effect.
Command to set screen brightness to 40% works:
sudo ddcutil setvcp 10 40 

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20241013
KDE Plasma Version: 6.2.0
KDE Frameworks Version: 6.7.0
Qt Version: 6.7.3
Kernel Version: 6.9.9-1-default (64-bit)
Graphics Platform: Wayland
Processors: 12 × AMD Ryzen 5 5600U with Radeon Graphics
Memory: 38,0 GiB of RAM
Graphics Processor: AMD Radeon Graphics
Manufacturer: LENOVO
Product Name: 20X70042CK
System Version: ThinkPad L15 Gen 2a

Comment 4 Arnab Bose 2024-10-19 02:43:10 UTC

For me, the lower brightness remains even with `ddcutil setvcp 10 30`. I can see brightness change with `ddcutil setvcp 10 40`, but the overall brightness still remains low.

It's as if there is something else independently changing the brightness of the screen, on top of ddcutil, only when KDE session is active.

Comment 5 Arnab Bose 2024-10-21 14:54:12 UTC

AFAICT, this is related or directly caused by this SDDM bug -
https://bugs.kde.org/show_bug.cgi?id=494894

I am not sure why, but probably SDDM has some kind of overlay which continues to persist.

Reason for believing that is the fact that once I switched to ly, I did not see this problem again so far.

Comment 6 Phil Hord 2024-10-21 17:28:15 UTC

I'm seeing similar, but for me it happens after logging in from screen-lock, possibly after laptop was suspended (but not always).  Usually it's both monitors (laptop and external), and the Brightness sliders usually match the actual brightness.  But today, for example, both monitors were dim, the laptop slider was at 0%, but the external slider was at 100%. So the external slider position did not match the actual monitor brightness.  

When I moved the sliders, each monitor reacted correctly.  So far, moving the sliders always corrects the problem for me.  

It would be useful if a dev could suggest some things to check to help with diagnosis.  Is there something in syslog?  Something to check in dbus?

Comment 7 Phil Hord 2024-10-21 17:29:05 UTC

Forgot to paste this:

Operating System: KDE neon 6.2
KDE Plasma Version: 6.2.0
KDE Frameworks Version: 6.6.0
Qt Version: 6.7.2
Kernel Version: 6.8.0-47-generic (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ i7-10610U CPU @ 1.80GHz
Memory: 15.3 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics
Manufacturer: LENOVO
Product Name: 20UCS4TR00
System Version: ThinkPad X1 Yoga Gen 5

Comment 8 Arnab Bose 2024-10-21 17:39:04 UTC

I have disabled sleep, hence I will miss if resuming from sleep also causes this, but sounds similar otherwise. 

IIRC resume reopens SDDM to log back in. If so it could still be an issue with SDDM.

Comment 9 danipo 2024-10-31 04:42:03 UTC

This sounds like a bug I'm experiencing. My screens are very dim on Wayland, normal brightness on X and on SDDM, rebooting doesn't seem to solve anything. 
Kernel: 6.11.5-gentoo-dist
Nvidia drivers: 565.57.01

I can increase the brightness to some extent using ddcutil set to 100 but it's still pretty dim.

kscreen-doctor always reports my brightness at 30% and changing it has no affect on what is reported in kscreen-doctor -o. 

HDR is disabled, I've tried with variable refresh on and off.

Comment 10 Oliver 2024-12-01 13:17:36 UTC

Operating System: CachyOS Linux 
KDE Plasma Version: 6.2.4
KDE Frameworks Version: 6.8.0
Qt Version: 6.8.0
Kernel Version: 6.12.1-1-cachyos-autofdo (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 5800X 8-Core Processor
Memory: 31.3 GiB of RAM
Graphics Processor: AMD Radeon RX 7800 XT

On waking from sleep brightness will drop to 30% - for me this seems to be the only condition that causes the brightness drop. Default settings used in Power Management though I've tried different settings in the past so I'm pretty sure it's nothing to do with Power Management. Desktop system powered via UPS.