Night mode is an automatic setting which takes advantage of the new wide-angle camera that's in the iPhone 11 and 11 Pro models. It's equipped with a larger sensor that is able to let in more light, allowing for brighter photos when the light is low.
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iPhone Media Event All But Confirmed for September 10
AllThingsD has an excellent track record with such reports, suggesting that the event will indeed take place on that date, but in case there was any doubt, The Loop's Jim Dalrymple is now confirming the report with a simple "Yep" post.
Dalrymple is well connected at Apple and has on many occasions either confirmed or refuted other reports and rumors in simple one-word posts with 100% accuracy. Such reports are generally taken as coming directly from Apple but delivered through an unofficial channel.
Official media invitations for the introduction should appear roughly a week before the event.