"Always Off" in fact means the feature is disabled entirely. The way to achieve your desired usage mode is to turn it on and then you can use the shortcuts to disable or enable it as needed.

Did I get that right, Natalie?

(In reply to Nate Graham from comment #1)
> "Always Off" in fact means the feature is disabled entirely. The way to
> achieve your desired usage mode is to turn it on and then you can use the
> shortcuts to disable or enable it as needed.
> 
> Did I get that right, Natalie?

Actually, I had tried that but even when I "turned it off" NL with the shortcut, every time I rebooted, NL was turned on by default.

That makes sense; probably the current on/off status when using the shortcut is only saved in memory, not to disk.

Re-opening since maybe there's more we should do to support this use case.

Yes, toggling Night Light with the keyboard shortcut or the switch in applet is only meant to suspend the feature temporarily, it will not persist across boots.  

Can you further explain your use case for turning on night light only occasionally but persisting across reboots? The idea of the existing toggle (suspend) feature is so you have an easy way to temporarily turn the blue light filter off if you need your screen colors to be neutral for a while e.g. for editing photos when otherwise you do want it on at your preferred times. But in what kinds of situations do you feel like turning on night light on or off at arbitrary times that it would be too annoying to go into the system settings with a click on the "Configure" button in the applet, or press a shortcut to suppress it again after a reboot?

A possibly relevant merge request was started @ https://invent.kde.org/plasma/kwin/-/merge_requests/5700

See also https://invent.kde.org/plasma/plasma-workspace/-/issues/114

I need NL depending on the ambient light and the content I am seeing, not on the time of the day. That is, at the same 10 PM, if the room is bright and I am watching a video, I don't need NL. But if the room is dark and I am reading text, then NL is useful because it reduces the perceived brightness lower than the lowest screen brightness (i.e., many screens lowest brightness is not low enough).

In my opinion, the current NL option seems unnecessarily confusing. On Android, I could set "Schedule" to "None", and use the "Use NL" toggle or a Quick Settings toggle to turn it on/off arbitrarily, and if I turn it on/off, it stays in that state even I reboot the phone. Of course, a phone doesn't reboot often, unlike a rolling Linux like Arch. I don't remember exactly, but I think Windows 10 probably also worked like this. Simple on/off without automatic scheduling.

The thing I did was setting Plasma's NL to "Always on" (because with "Always off", the shortcut did not work) and used the shortcut to turn it off/on, but the state was not remembered and when I rebooted the PC in a bright room, NL got automatically turned on at the next login. Of course, all I had to do was pressing the shortcut to turn it off, but I thought it was annoying.

So, what I think is, any of the following change could be helpful to people who want only manual control, without automatic anything.

(1) When NL is set to  "Always off", pressing the NL shortcut change it to "Always on", and when it is set to "Always off", the shortcut changes it to "Always off".
(2) NL "Switching times" can have a new entry "Manual". The shortcut turns it on/off, and it persists after reboot.
(3)  When NL is set to  "Always on", and the user pressed the NL shortcut to turn it off, the off state persists after reboot.

Git commit 6ec7e919fb9f7fe80221810da4f7efe6d56ebf4a by Natalie Clarius.
Committed on 06/05/2024 at 23:14.
Pushed by nclarius into branch 'master'.

plugins/nightlight: clarify strings for inhibition

To clarify that the toggle action merely temporarily disables the blue light filter, rather than turning the schedule off permanently like the "Disbaled" setting in the KCM does, use "suspend/resume" terminology instead of "off/on" in the keyboard shortcut and OSD.

Follow-up on plasma-workspace!4262

M  +3    -3    src/plugins/nightlight/nightlightmanager.cpp

https://invent.kde.org/plasma/kwin/-/commit/6ec7e919fb9f7fe80221810da4f7efe6d56ebf4a

Okay, seem reasonable enough.  

It sounds to be like this use case would be even better addressed by adding support for activating night light based on an ambient light sensor, in addition to the ability to temporarily turn it off manually (eg for watching a video). But that would of course only work on devices that actually have an ambient light sensor. So maybe adding a "Manual mode" makes sense anyway.

Sadly there are still lots of laptop hardware without ambient light sensors. My laptop is a pretty premium one (though admittedly 4 years old) and it doesn't have an ALS.

This is annoying since every Apple laptop has had an ALS since like 2005. This stuff is not exactly rocket surgery!  But I guess it is for the rest of the PC industry.

(In reply to Natalie Clarius from comment #9)
> Okay, seem reasonable enough.  
> 
> It sounds to be like this use case would be even better addressed by adding
> support for activating night light based on an ambient light sensor, in
> addition to the ability to temporarily turn it off manually (eg for watching
> a video). But that would of course only work on devices that actually have
> an ambient light sensor. So maybe adding a "Manual mode" makes sense anyway.

I have a similar use case like Sin Jeong-hun and a manual mode is definitely needed to make the feature more useful and flexible, it would make the feature behave similarly to Windows 11 and Android which is probably what most users expect as there is a lot more criteria that determines the use of the blue light filter than simply scheduling.

I'd really like a proper manual mode as well. At the very least it should be made clear what the "always off" option does by renaming it to something like "disabled" instead, because it's really confusing having a Night Light keyboard shortcut that does absolutely nothing on purpose.