Viewing the screen of your iPhone or iPad at night can be tiring on the eyes. Additionally, some studies report that blue light emissions can keep you awake, which is why iOS includes a clever display mode called Night Shift which warms the display, making it easier on your eyes.
To schedule Night Shift to automatically turn on every day at sunset – then turn off again in the morning, go to Settings > Display & Brightness > Night Shift, then toggle the Scheduled switch on. Next, use the From and To fields to set the time that best suits your needs. You can also adjust the strength and warmness of Night Shift by sliding the Color Temperature button at the bottom of the screen.