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.
macOS Catalina Now Available
Apple Seeds First Beta of iOS 11.4.1 to Developers
Registered developers can download the new iOS 11.4.1 beta from Apple's Developer Center or over-the-air once the proper configuration profile has been installed from the Developer Center.
We don't know what new features are included in the iOS 11.4.1 beta, but it is likely to focus on bug fixes and performance improvements to address issues discovered since the release of iOS 11.4.
Apple's work on iOS 11 is wrapping up, as iOS 12 is set to be released to developers next week following the keynote event of the 2018 Worldwide Developers Conference.