The sensor is not in the camera. It is just to the left of it. If you look very closely, you will see the almost-microscopic holes in the aluminum which hide the sensor.
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As for the backlighting
you need to be sure the brightness is set manually to whatever level you wish first. If you have it turned all the way down, then when you go into a dark area, it will appear that the light is not coming on.
Basically you can tell if it is working if the manual buttons adjust the light. If the computer detects that it is bright enough to not need the light, the manual buttons won't do anything except pop up an icon telling you it isn't working.