Many people prefer the night mode, so I don't know if linking to day-night is the best option.
I agree with that SBK74, I personnaly stay in Dark mode also, as I can't see anything in day with the Light mode
Here is what I think would suit the most regarding light settings:
Basically switching from day to night should keep the dark mode but dim respectively (Screen + Leds) from day% to night%
with those settings :
Day% as a user setting for max luminosity for screen and leds
Night% as a user setting for min luminosity for screen and leds
Dark/Light/Auto as a user setting for Auto switch between Dark or Light mode for screen
On / Off as a user setting for Auto switch from Day/Night %