[MarcinM]

There are 2 sensors to the left of the top speaker when the phone is facing you, face forward.
When you cover one of them the screen-brightness is changing due to different light exposure detection meaning further left sensor is light sentitive. The other sensor to the right of the first one is lighting up when you're using some of your apps like google store for example, and under specific angle you can see redish light flashing under the black glass, looks like a cat eyes when they reflect the light in the darkness or like a TV pilot IR light that can be seen when recorded with camera. You can see and feel the light flashing of your iris under the right angle.