The Windows Hello facial recognition system can no longer be used in the dark. This has been confirmed by Microsoft itself, with it actually being disabled through an update released in April. Previously, Windows Hello could be used in the dark if the PC was equipped with an infrared camera system.
This feature was disabled by Microsoft to patch a security vulnerability discovered by Nanyang University where the security system could be bypassed when the camera was used in the dark. Windows Hello facial recognition can still be used, but only in bright lighting situations.
It now requires facial verification from the infrared camera and color webcam simultaneously before the computer can be unlocked. Although the system has been disabled since April, it was only noticed when a handful of Surface users reported this issue, according to a Windows Central report.