Night Shift is a built in software feature of iOS and macOS.
[3] Apple claims that the feature may help users have a better night's sleep by filtering blue wavelengths from the display, which suppress melatonin biosynthesis.
[5][6] Changing the color temperature of the display from blue towards yellow (without dimming the screen) was shown to have no effect on sleep outcomes (sleep latency, duration, efficiency and wake after sleep onset) in a 2021 study on 167 college undergraduates[7] and to be insufficient for preventing the impact on melatonin suppression.
[12] The feature can be turned on in Settings (in iOS)[13] and in System Preferences (in macOS)[12] and can be toggled on or off manually in the Notification Center (in macOS)[14] or in the Control Center (in iOS).
[16] The user can also customize the intensity of Night Shift in Settings (iOS)[2] or System Preferences (macOS).