As above. If the display has gone into night mode because the lights have gone on during the day, twisting the trip reset clockwise overrides that and brightens the display again. It then remembers that and stays in day mode at night. When the lights are on, twist it anti-clockwise to dim the display again, that should restore normality. It's a daft system, it would be better to use a sensor in the cabin to control the display brightness rather than just checking whether the lights are on or not.
Alan.