How does the proximity sensors on smartphone makes the main screen blank its internal working on phone?How does the proximity sensors on smartphone makes the main screen blank its internal working on phone?

Descriptions

How does the proximity sensors on smartphone makes the main screen blank its internal working on phone?How does the proximity sensors on smartphone makes the main screen blank its internal working on phone?

ANSWER 

 The proximity sensor usually sits up near the top speaker and combines an infrared LED and light detector to work out when you have the phone up to your ear, so that screen can be switched off. The sensor emits a beam of light that gets bounced back, though it's invisible to the human eye.The proximity sensor usually sits up near the top speaker and combines an infrared LED and light detector to work out when you have the phone up to your ear, so that screen can be switched off. The sensor emits a beam of light that gets bounced back, though it's invisible to the human eye.