[ulysses]

i think you're talking about the light sensor. looking at the "ear-hole" on the phone, it's to the left? i don't know what ALL it does. i think one of it's functinoes is to turn the screen off when you have the phone to your face so you don't push buttons with chubby cheeks. also if you have the auto dim function on in your settings, it will change the brightness of your screen depending on "background light"