iOS 9.3 is coming in the Spring and will introduce Night Shift as well as a number of other new features.
Apple Begins Prepping Yerba Buena Center for iPhone 5 Media Event
Apple's media event begins at 10:00 AM Pacific Time / 1:00 PM Eastern Time on Wednesday, September 12.
Update: BusinessInsider has photos at a later stage.
Update 2: MacStories has more photos: