Why the IR Lights on iPhone/iPad Pro 2018 (Face ID) are always on? (Explanation)

I've seen too many times people asking the same question here and on other foruns... I have the answer.

First off all... All iPhones have IR proximity sensors... and the newer ones... they got the flood iluminator and dot projector. But why the IR light is always flashing even I'm not on a call or using Face ID?

The proximity sensor is always on to determine if the light sensor is being covered or the ambient that you are in is really dark.

Test by yourself... put a flashlight direct to your iPhone... it will increase the brightness, and if you cover the notch (or earspeaker on the older ones) with your finger, the phone will not lower the brightness unless you take your finger off the notch.