Along with major enhancements like built-in GPS and swim workouts, the Apple Watch Series 2 includes another unique new feature which allows you to gradually wake the screen using the Digital Crown — essentially letting you sort of “peek” at it.
The setting to enable this can be found under General, Wake Screen in the Apple Watch app on your iPhone, although oddly it’s not present in the corresponding section in the watchOS Settings app — you have to enable it from your iPhone.
With this option enabled, turning the Digital Crown upward when your Apple Watch is asleep will gradually illuminate the screen while keeping its brightness low — useful for glancing at your Watch in low light conditions, such as in a movie theater.
Turning the Digital Crown back the other way will put the screen back to sleep, provided you haven’t reached peak brightness.