Ghost light!

[tat21985]

Last night,as I was browsing Tumblr, I noticed a very faint red light come on to that was to the immediate right and just below the speaker.. I had never seen this before, and haven't seen it again today.. Does anyone have any idea what it could be, what the purpose of it is?

 

[Subsound]

I have seen this other phones. I forget which one it is, but it is either a light sensor or proximity sensor. The light sensor is for the auto brightness on the screen and the proximity sensor is used to turn off the screen while the phone is against your ear while on a call.