Bug 511226

Summary:	External screen stays dimmed after "dim/off/on" idle cycle
Product:	[Plasma] plasmashell	Reporter:	Konstantin Kharlamov <Hi-Angel>
Component:	Power management & brightness	Assignee:	Plasma Bugs List <plasma-bugs-null>
Status:	REPORTED ---
Severity:	normal	CC:	nate
Priority:	NOR
Version First Reported In:	6.5.0
Target Milestone:	1.0
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description Konstantin Kharlamov 2025-10-27 17:06:44 UTC

SUMMARY

Given sequence of events: 1. external screen is dimmed, 2. external screen turned off on idle, 3. external screen turned on due to quitting from idle; you'll find external screen being still being dim.

Having debugged Powerdevil, I see that the pre-dim brightness value is being set correctly. I presume what happens is that when the screen turns on (which happens with ≈1 sec delay), Powerdevil sends brightness change before the screen is on, and screen simply ignores the setting. Presumably brightness should be set after the screen is on.

However, this part of code I don't know, so that this point I'm reporting a bug.

STEPS TO REPRODUCE
1. Connect external screen to a laptop
2. Wait for external screen to dim
3. Wait for external screen to turn off
4. Poke a mouse to wake the screen up and observe the brightness

OBSERVED RESULT

Screen is still dimmed

EXPECTED RESULT

Screen should have pre-dim brightness

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.5.0
KDE Frameworks Version: 6.19.0
Qt Version: 6.10.0
Kernel Version: 6.17.5-arch1-1 (64-bit)
Graphics Platform: X11
Processors: 12 × Intel® Core™ i5-10500H CPU @ 2.50GHz
Memory: 16 GiB of RAM (15.3 GiB usable)
Graphics Processor 1: Intel® UHD Graphics
Graphics Processor 2: NVIDIA GeForce RTX 3050 Ti Laptop GPU

Comment 1 Nate Graham 2025-10-29 18:29:58 UTC

Is it a regression in Plasma 6.5? Or has it been like this for longer?

Comment 2 Konstantin Kharlamov 2025-10-29 18:33:12 UTC

(In reply to Nate Graham from comment #1)
> Is it a regression in Plasma 6.5? Or has it been like this for longer?

I don't think it's a regression, I feel I've seen this ever since external monitor brightness modification was added. It's just I haven't used external monitor to often until recently, so never minded it.

Comment 3 Konstantin Kharlamov 2025-10-29 18:44:47 UTC

(In reply to Konstantin Kharlamov from comment #2)
> It's just I haven't used external monitor to often until recently, so never minded it.

…and also because I have a habit of pressing a keybind to turn displays off before going away (brought in from mobile devices), which was skipping the dimming part of the cycle.