Anti-glare Rear View Mirror Auto Mode Indicator

[Chris Parker]

My wife has a 2008 Lexus RX350.

My rear view mirror has two green indicators on it to the left and right of the on/off button for the compass and anti-glare auto mode. However, strangely, only the left green indicator lights up. There is only one anti-glare sensor on the back of the rear view mirror. What is the right green indicator for, and why is it always off?

[Pangloss]

Isn't that actually a sensor too, for the light hitting the surface of the mirror?