Bug 472456

Summary:	Laptop wakes up from screen saving mode in full brightness
Product:	[Plasma] plasmashell	Reporter:	Marián Konček <koncek.marian>
Component:	Power management & brightness	Assignee:	Plasma Bugs List <plasma-bugs-null>
Status:	RESOLVED INTENTIONAL
Severity:	normal	CC:	gavsiu, jpetso, kdedev, natalie_clarius, nate, xaver.hugl
Priority:	NOR
Version First Reported In:	5.27.6
Target Milestone:	1.0
Platform:	Other
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description Marián Konček 2023-07-21 06:38:58 UTC

SUMMARY
When lowering a laptop's brightness to a minimum (i. e. 0 %) by pressing the Fn keys, waiting for the screen saving (which turns off the screen) mode to activate and then moving the mouse to wake the screen, the screen has maximum brightness.

It is worth mentioning that changing the brightness with Fn keys behaves as-if the brighntess was at 0 %. I. e. lowering the brightness goes to 0 %, increasing it goes to 5 %.

When the brightness is above 0 %, then it wakes up to the correct previous brightness.
This behaviour was also different some ~ 2 years ago, when the screen would wake up to the 5 % (?) or some other small value that was not 0 %.

STEPS TO REPRODUCE
1. On a laptop, manually lower the screen's brightness to 0 %. (The screen is now almost completely black)
2. Wait for the screen saving mode to turn off the screen (not sleep, not screen dim)
3. Perform any action that wakes up the screen. (e. g. move mouse)

OBSERVED RESULT
Laptop screen now has 100 % brightness.

EXPECTED RESULT
Screen should wake up with the minimal **user-visible** screen brightness, i. e. one Fn button press away from 0 %. Which usually is 5 %.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Fedora KDE 38
(available in About System)
KDE Plasma Version: 5.27.6
KDE Frameworks Version: 5.107.0
Qt Version: 5.15.10

ADDITIONAL INFORMATION
This issue was observer first time a few years ago.
Behaviour is the same on X11 and Wayland.
Behaviour is the same no matter whether external monitors are connected.

Comment 1 Natalie Clarius 2023-08-10 21:00:10 UTC

Can confirm that this is the observed behavior, but I don't understand the motivation for what you consider the expected behavior. I can see how one might find it would make sense for the previous brightness to be restored (which would be 0% in your scenario). I can also see the rationale behind the current behavior that on wakeup, the screen should not just stay off so the alternative is to toggle it to full brightness instead. But why should it be neither full brightness nor what was previously manually set but something in between (5%)?

Comment 2 Marián Konček 2023-08-12 18:15:02 UTC

My argument is that for some (most ?) Linux laptops, having brightness at 0 % means that the screen is more-less completely black. Waking up the screen from screen saving mode could not be visible to the user. (I am aware that setting "acpi_osi=Windows 2015" kernel parameter changes the range of brighntess settings but I am accustomed to the current behaviour.)

Another argument is that the behaviour I was describing was in KDE maybe up until 2-3 years ago. I have wanted to submit this for a long time but got to it only now. I could try to look up some Fedora version for which that was the case...

Comment 3 Bug Janitor Service 2023-08-27 03:45:17 UTC

Dear Bug Submitter,

This bug has been in NEEDSINFO status with no change for at least
15 days. Please provide the requested information as soon as
possible and set the bug status as REPORTED. Due to regular bug
tracker maintenance, if the bug is still in NEEDSINFO status with
no change in 30 days the bug will be closed as RESOLVED > WORKSFORME
due to lack of needed information.

For more information about our bug triaging procedures please read the
wiki located here:
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If you have already provided the requested information, please
mark the bug as REPORTED so that the KDE team knows that the bug is
ready to be confirmed.

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

Comment 4 Nate Graham 2023-09-01 16:23:32 UTC

FWIW, in Plasma 6, 0% brightness will no longer turns the backlight off complete on some hardware. So that part is now moot.

Comment 5 Natalie Clarius 2023-09-10 10:09:12 UTC

*** Bug 474355 has been marked as a duplicate of this bug. ***

Comment 6 Nate Graham 2023-09-10 13:30:12 UTC

*** Bug 474355 has been marked as a duplicate of this bug. ***

Comment 7 Jakob Petsovits 2023-12-03 05:56:46 UTC

My expectation would be that if I change the brightness via Fn keys or Brightness applet, that the brightness level is preserved across suspend and restarts. In other words, changing brightness should (imho) set the value in the config file.

Things get a little more complex once we consider that different battery levels (and plugged-in) can have different brightness levels assigned. Even then, I'd feel more comfortable knowing that I don't have to go into System Settings to preserve the brightness that I just empirically fine-tuned via OSD.

Comment 8 Natalie Clarius 2023-12-05 01:11:18 UTC

(In reply to Marián Konček from comment #2)
> My argument is that for some (most ?) Linux laptops, having brightness at 0
> % means that the screen is more-less completely black. Waking up the screen
> from screen saving mode could not be visible to the user.

As Nate wrote, having the brightness at 0% completely black through brightness keys will no longer be a thing in Plasma 6, so is there any remaining case where the current behavior would be an issue?

Comment 9 Marián Konček 2023-12-05 07:30:09 UTC

I don't think so, I guess I will have to get used to it.
Truth is, I opened the bug because I noticed the behaviour changed from what I was used to.

Comment 10 TraceyC 2025-03-06 21:12:12 UTC

I'm going to close this, since the behavior of the feature was changed. If you have any other problems with brightness on your laptop, please open a new report. Thanks.