Samsung
Toggle Screen Brighten for Face Recognition auf Samsung
Face recognition on Samsung phones needs enough light on your face to work reliably. In low-light conditions, the system briefly raises the display brightness right before scanning, independent of your manual brightness slider or adaptive brightness setting.
This is controlled by a dedicated toggle called Brighten screen inside the Face recognition settings. When enabled, every face unlock attempt in the dark triggers a short flash of light from the screen. When disabled, the display stays at its current brightness during unlock attempts, which can make face recognition less accurate at night but avoids the sudden flash.
Menu path
Go to Tap on Settings ➔ Tap on Biometrics and security ➔ Tap on Face recognition ➔ Enter the current Pattern, PIN or Password ➔ Enable or disable Brighten screen.
You need your current screen lock credential to enter the Face recognition menu, since this section also lets you re-register your face or remove it entirely. If face unlock struggles in the dark after disabling this option, turning it back on usually solves the issue immediately.