Bug 506946

Summary:	KDE backlight on laptop screen gets max brightness wrong
Product:	[Plasma] plasmashell	Reporter:	Vorpal <kdebugs>
Component:	Power management & brightness	Assignee:	Plasma Bugs List <plasma-bugs-null>
Status:	RESOLVED WORKSFORME
Severity:	normal	CC:	kdedev, natalie_clarius, nate
Priority:	NOR	Keywords:	multiscreen
Version First Reported In:	6.4.2
Target Milestone:	1.0
Platform:	Arch Linux
OS:	Linux
See Also:	https://bugs.kde.org/show_bug.cgi?id=494577
Latest Commit:		Version Fixed In:
Sentry Crash Report:

Description Vorpal 2025-07-12 10:40:59 UTC

SUMMARY
I often use my laptop with external monitors. Recently screen backlight has started to work for external monitors too. However, after a while (days) the max brightness on the laptop monitor keeps going down. That is 100% according to KDE is not 100%. The external monitors are unaffected. This keeps slowly degrading over time, over many suspend/resume cycles.

root /sys/class/backlight/intel_backlight ❯ cat /sys/class/backlight/intel_backlight/brightness
455
root /sys/class/backlight/intel_backlight ❯ cat /sys/class/backlight/intel_backlight/max_brightness
1515

Yet Plasma claims this is 100%. If I manually write a higher value it works, until I try to change it with plasma again, after which it keeps being broken.

For now I would be happy with a workaround where I disable KDE handling backlight at all, if that is possible.

STEPS TO REPRODUCE
1. I have no idea. My best guess is: Use the computer over several days to weeks, connecting and disconnecting external displays, putting the laptop in suspend and resuming it.
2. Watch it degrade.

OBSERVED RESULT
Max brightness keeps going down

EXPECTED RESULT
100% brightness should keep being 100% brightness.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch Linux
KDE Plasma Version: 6.4.2
KDE Frameworks Version: 6.15.0
Qt Version: 6.9.1

* Kernel Version: 6.15.3-zen1-1-zen (64-bit)
* Graphics Platform: Wayland
* Processors: Intel® Core™ i7-8550U CPU @ 1.80GHz (4 cores, 8 threads)
* Memory: 32 GiB of RAM (31.0 GiB usable)
* Graphics Processor: Intel® UHD Graphics 620

ADDITIONAL INFORMATION

Lenovo Thinkpad T480
External monitors using Display Port with USB C adapter and HDMI (one of each).

Comment 1 TraceyC 2025-07-21 17:13:27 UTC

This looks related to bug 494577. The difference here is that the laptop display is affected, in the other bug it was an external monitor. Also, that the brightness goes down with each suspend/resume cycle.

Comment 2 Nate Graham 2025-08-19 23:01:10 UTC

Is the screen HDR-capable? `kscreen-doctor -o` will tell you. If it is, it's possible that 455 or so is the maximum *SDR* brightness and 1515 is the maximum *HDR* brightness.

Comment 3 Bug Janitor Service 2025-09-03 03:48:18 UTC

🐛🧹 ⚠️ This bug has been in NEEDSINFO status with no change for at least 15 days. Please provide the requested information, then set the bug status to REPORTED. If there is no change for at least 30 days, it will be automatically closed as RESOLVED WORKSFORME.

For more information about our bug triaging procedures, please read https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging.

Thank you for helping us make KDE software even better for everyone!

Comment 4 Bug Janitor Service 2025-09-18 03:48:47 UTC

🐛🧹 This bug has been in NEEDSINFO status with no change for at least 30 days. Closing as RESOLVED WORKSFORME.