Summary: When a laptop is shut down while running on battery power, the screen brightness level from the battery profile is incorrectly retained upon the next boot, even if the device is connected to AC power before turning it on. The system fails to apply the brightness settings configured for the "On AC Power" profile at startup. This issue is exacerbated by the inability to adjust screen brightness at the SDDM login screen, a known issue tracked under bug report #417237. This leaves the user with a potentially very dim and unusable screen until they have logged in and can manually adjust the brightness. Steps to Reproduce: 1. **Configure different brightness levels for battery and AC power:** * Navigate to `System Settings > Power Management > Energy Saving`. * On the **On Battery** tab, set a specific screen brightness, for example, 30%. * On the **On AC Power** tab, set a different, higher brightness level, for example, 80%. 2. **Operate and shut down on battery:** * Disconnect the AC adapter and let the laptop run on battery power. The screen brightness should adjust to the level set for the battery profile (e.g., 30%). * With the laptop still on battery power, perform a full shutdown. 3. **Boot up on AC power:** * Connect the AC adapter to the laptop while it is powered off. * Power on the laptop. Observed Result: The screen brightness at the SDDM login screen and after logging into the Plasma session remains at the level that was active when the device was shut down on battery power (e.g., 30%). The system does not apply the brightness level configured for the "On AC Power" profile (e.g., 80%). Expected Result: When the laptop is booted while connected to AC power, the system should detect the AC power state and apply the corresponding brightness setting (e.g., 80%) at startup or, at the latest, upon reaching the login screen. Additional Information: This behavior appears to be closely related to Bug #497362, which has been reported and marked as **RESOLVED FIXED** in Plasma 6.3. The underlying cause was identified as PowerDevil failing to apply the correct profile at startup on Wayland because the display output was not yet available when the profile change was processed. The inability to adjust brightness at the SDDM login screen (Bug #417237) makes this primary issue more impactful, as users who had a low brightness setting on battery are forced to navigate the login process with a very dim screen. Software/OS Versions: Operating System: Arch Linux KDE Plasma Version: 6.3.5 KDE Frameworks Version: 6.14.0 Qt Version: 6.9.1 Kernel Version: 6.12.33-1-lts (64-bit) Graphics Platform: Wayland Processors: 12 × Intel® Core™ i7-10750H CPU @ 2.60GHz Memory: 15.4 GiB of RAM Graphics Processor 1: NVIDIA GeForce GTX 1650 Graphics Processor 2: Intel® UHD Graphics Manufacturer: LENOVO Product Name: 82CG System Version: IdeaPad Gaming 3 15IMH05
I need to clarify one thing, the incorrect brightness only occurs before logging into SDDM. After logging in, the brightness is automatically corrected by the power management. So the expected behavior here is that the brightness is adjusted by the power settings even before logging in, at the risk of the user not being able to log in with the brightness low and unable to increase it on the SDDM screen.
This is one of those issues that's not really fixable as long as we continue using SDDM, because SDDM would need to launch powerdevil, which means it would need to accumulate KDE-specific code, which means it would no longer really be desktop-agnostic, which means it's not really something SDDM wants to do. It's for this reason that we've been working on a replacement greeter that is KDE-specific. In there, we can fix issues like this one.