Dimming


Glare from a following vehicle's headlamps in a rear view mirror
A prismatic rear-view mirror â sometimes called a "day/night mirror" â can be tilted to reduce the brightness and glare of lights, mostly for headlights shining directly on the eye level at night. This type of mirror is made of a piece of glass that is wedge-shaped in cross sectionâits front and rear surfaces are not parallel.
On manual tilt versions, a tab is used to adjust the mirror between "day" and "night" positions. In the day view position, the front surface is tilted and the reflective back side gives a strong reflection. When the mirror is moved to the night view position, its reflectorized rear surface is tilted out of line with the driver's view. This view is actually a reflection off the non-reflectorized front surface. Since the non-reflectorized front surface allows most of the light to go through, only a small amount of light is reflected into the driver's eyes.
Automatic dimming
In the 1950s, American inventor Jacob Rabinow developed a light-sensitive automatic mechanism for the wedge-type day/night mirror.<SUP id=cite_ref-4 class=reference>[5]</SUP> Several Chrysler Corporation cars offered these automatic mirrors as optional equipment as early as 1959, but few customers ordered them for their cars and the item was soon withdrawn from the option lists.<SUP style="WHITE-SPACE: nowrap" class=Template-Fact title="This claim needs references to reliable sources from June 2011">[citation needed]</SUP> Several automakers<SUP style="WHITE-SPACE: nowrap" class="noprint Inline-Template" title="You can help -- from June 2011">[vague]</SUP> began offering rear-view mirrors with automatic dimming again in 1983,<SUP style="WHITE-SPACE: nowrap" class=Template-Fact title="This claim needs references to reliable sources from June 2011">[citation needed]</SUP> and it was in the late 1980s that they began to catch on in popularity.<SUP style="WHITE-SPACE: nowrap" class=Template-Fact title="This claim needs references to reliable sources from June 2011">[citation needed]</SUP>
Current systems usually use photo sensors mounted in the actual rear-view mirror to detect light and dim the mirror by means of electrochromism. This electrochromic feature has been also incorporated into side-view mirrors allowing them to dim and reduce glare as well.