Based on each signal, the control unit judges whether the light at the rear of the vehicle is stronger than the light sensed at the front. If the control unit judges that the light sensed by the rear-facing lux level sensor is brighter than the light sensed by the front-facing lux level sensor, it transmits a signal relaying that information to the drive circuit.

When shifting the transmission to the R position/mode while automatic dimming control is in operation, the automatic dimming turns off and the mirror returns to its highest state of reflectivity. When shifting the transmission out of the R position/mode, the automatic dimming control function is reactivated.