But that's just theory, in practice users don't squint their eyes when they use your UI, meaning that in practice perceived brightness does matter, less how it comes about.
My point was that luminance and chromacity fulfill a very similar function in UI design besides size or shadows, they bring elements forward, make them stand out. An item with low chromacity therefore isn't on the same Z level as an item with high chromacity if you think of the foreground and background as a 3d space that you can use to guide the eyes of users. It's the function for the user experience that counts, at least for me.
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But that's just theory, in practice users don't squint their eyes when they use your UI, meaning that in practice perceived brightness does matter, less how it comes about.
Isn’t the perceived brightness depend on surrounding colors and many other variables such as motion, incident illumination, etc?
Those things cannot be part of a specification such as CIE or NCS.
My point was that luminance and chromacity fulfill a very similar function in UI design besides size or shadows, they bring elements forward, make them stand out. An item with low chromacity therefore isn't on the same Z level as an item with high chromacity if you think of the foreground and background as a 3d space that you can use to guide the eyes of users. It's the function for the user experience that counts, at least for me.
Thanks for the discussion, I learned about the NCS system and you seem to know a lot about this.
For psychological impact use of "brightness", yes.
For judging contrast against e.g. text for legibility in a design?