Apple wants to help you avoid ‘luminescence shock’ on iPhones, Apple Watches — Apple World Today

Apple’s idea is for a luminescence shock avoidance algorithm that selectively limits the brightness level of an iPhone or Apple Watch when the display device is activated in a dark environment to prevent the temporary vision impairment that can occur when a display device is activated in a dark environment. 

The algorithm receives the state of the display (e.g. on or in standby mode), and can optionally receive an ambient lighting value from an ambient light sensor and a user-selectable manual brightness adjustment setting to determine whether luminescence shock avoidance should even be triggered, and if it is triggered, how much should the brightness level of the display be limited.