what is the tiny LED beside the proximity sensor?

[flipteg]

i have always assumed that there is only the notification LED beside the proximity sensor. when i woke up this morning, there was a very faint red LED next to the bigger notification LED. i have never seen this before and i didn't know how it turned on or how to turn it off. when i rebooted the phone, it immediately shut off and didn't turn on again. when i looked at the phone closely, there is indeed 3 holes there: the notification LED, proximity sensor, and this LED i'm trying to identify.

 

[Cyber Warrior]

It's a sensor that turns your phone off when held up to your face. The 3 holes you are seeing are the LED notification, Proximity sensor and Light detection.

 

[flipteg]

thanks for the reply! it just confused me because i never seen it lit up before, albeit a very dim light.