Microsoft is currently testing a system-level night mode for Xbox consoles, with users in the Xbox Insiders Alpha Skip-Ahead ring having access to the options right now.
The new update will give you the ability to set schedules for when your console goes into night, including manually scheduling and automatic scheduling according to your time zone’s sunrise and sunset times. In night mode you can set several parameters to make gaming in the dark more comfortable, such as an adjustable blue light filter (which can affect your ability to fall asleep) and the overall brightness of the image sent to your display.