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