Owner's Manual for the vehicle. With a quick reference ... - E38.org

188nRearview mirror with automatic dimmer
390de113
The semisolid reacts chemically to this
electrical current, thus providing infinitely-variable
dimming of the mirror
(electrochromic technology).
As a result, it is no longer necessary to
dim the mirror manually, and the driver
can maintain full concentration on traffic.
The interior rearview mirror with automatic
dimming feature reduces glare
from following traffic by adapting the intensity
of the reflected images to correspond
to levels of light registered by the
unit's sensors. The mirror reverts to its
undimmed setting as soon as the light
source disappears. One of these sensors
is mounted on the front of the mirror
housing and is designed to monitor
light levels in the area immediately forward
of the vehicle. The second sensor
is integrated within the mirror's glass.
The electronic control system operates
by comparing the respective levels of
luminous intensity in front of and behind
the car. The difference provides the basic
parameter used to modulate an
electrical current and induce chemical
changes in a semisolid layer incorporated
in the lens.