Lexus RX300 2003 Owner's Manual page 119

When the inside rear view mirror surface changes, the outside
rear view mirror surfaces will also become darker.
When the ignition key is inserted and turned on, the inside rear
view mirror always turns on in the AUTO mode.
When the outside air temperature is low, it may take a little
longer for the mirror to darken in response to the detection of
headlights.
CAUTION
Do not adjust the mirror while the vehicle is moving.
Doing so may cause the driver to mishandle the vehicle
and an accident may occur resulting in death or serious
injuries.
16R380
To ensure correct functioning of an anti–glare mirror
sensor located on the back side of the mirror, do not touch
or cover the sensor with your finger or a piece of cloth, etc.