Bug 516061

Summary: Temperature slider should have lower temperatures to the left and higher on the right
Product: [Applications] systemsettings Reporter: Riccardo Robecchi <sephiroth_pk>
Component: kcm_nightcolorAssignee: Plasma Bugs List <plasma-bugs-null>
Status: RESOLVED INTENTIONAL    
Severity: normal CC: kwin-bugs-null, olib141
Priority: NOR    
Version First Reported In: 6.5.5   
Target Milestone: ---   
Platform: Arch Linux   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description Riccardo Robecchi 2026-02-15 22:29:14 UTC
SUMMARY
Currently, the temperature sliders for night and day temperatures show higher temperatures on the left hand side and lower temperatures on the right hand side. This is, however, quite confusing, as the temperatures are ordered contrary to the normal progression of numbers (which is left to right, at least in English and other Western languages/traditions). While I do understand that the slider is meant to symbolise the strength of the effect, the addition of the numbers and their ordering contrary to conventions becomes confusing.
The solution here would be to either keep the current arrangement but remove the numbers to make the slider a simple intensity control (which, however, is unadvisable as it removes precision) or to turn around the way the slider works, with higher temperatures on the right hand side.

STEPS TO REPRODUCE
1. Open the KCM

OBSERVED RESULT
Higher temperatures are on the left hand side of the sliders, lower temperatures are on the right hand side.

EXPECTED RESULT
Temperatures are ordered according to the normal ordering of numbers, and therefore with higher numbers being placed on the right hand side.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Endeavour OS (Arch Linux)
KDE Plasma Version: 6.5.5
KDE Frameworks Version: 6.22.0
Qt Version: 6.10.2

ADDITIONAL INFORMATION
Comment 1 Oliver Beard 2026-02-16 14:20:48 UTC
I believe it makes sense for the slider to represent the strength of the effect, as 0% represents no change and 100% represents '(fully) on'. Removing the numbers to clarify that the sliders do not directly represent colour temperature would likely be objectionable as users might want to set specific values (perhaps for consistency with other systems).

This could be improved with a custom slider that does represent colour temperature, visually. This is unfortunately not practicable, so I will mark this as RESOLVED INTENTIONAL.
Comment 2 Riccardo Robecchi 2026-02-16 16:23:35 UTC
It does, but only if you remove the numbers. For comparison's sake, let's look at what other systems and applications do:
- GNOME has a slider that goes from cool to warm, but it presents this graphically and omits numbers
- Cinnamon has a similar approach: graphical representation from cool to warm
- Windows 10 has a slider from warm to cool, with a graphical representation of this, but with no numbers
- Windows 11 provides a clearly labelled "strength" slider with no numbers
- macOS calls the feature "night shift" and provides the third example of a slider where strength increases going to the right, without any numbers
- Android only shows an intensity slider like Windows 11

It looks like all other platforms do not use numbers and order from cool to warm (save for now-EOL Windows 10).

All applications where colour temperature numbers are used, however, use the number ordering as intended:
- All Redshift GUI implementations I found use numbers and correctly order them
- f.lux provides numbers and correctly orders them
- LightBulb (Windows) provides numbers and correctly orders them
- SunsetScreen (Windows) provides numbers and correctly orders them
- Twilight (Android) provides an unlabelled intensity slider
- Red Moon (Android) provides numbers and correctly orders them
- broadening the view, GIMP provides a colour temperature adjustment feature with correct LTR ordering

It looks like there are no consistency concerns with other systems, given how every single other OS and DE does not provide numbers. All applications which provide numbers, however, also correctly order them. I have not been able to find an example of a night light feature which operates like Plasma currently does. If consistency is a concern, then I suggest changing the current behaviour as it is inconsistent with every single other system and application, irrespective of what they do.
Comment 3 Riccardo Robecchi 2026-02-16 16:24:54 UTC
macOS is obviously the fourth example. I added Cinnamon before it and forgot to update the text; sorry about that!