How do they work automatically? I suppose it has something to do with light sensors, but how does it just work on the few “pixels” of headlights and not the entire image?
There are two reflective surfaces on an auto rear view mirror. One is the silver on the back of the glass, and one is the front surface. These surfaces are not parallel. When bright lights against darkness are all you really need to see, the surface of the glass is sufficient. When you want to see detail in daylight, the silvered surface is used. By positioning the mirror, you are able to use the silver when you want, and the surface reflection is easily ignored. At night, you aim the harsh glare of the silvered refelction out of your eyes, and the remaining reflection still shows you the position of the headlights behind you.
Tris
Just to be thorough, here’s a Cecil Link™: How do “night” rear view mirrors work?.
I hope I’m not mis-interpreting the OP,seth,but I take it you mean the electrochromic mirrors.Here’s a link to some info on Gentex,the first company manufacture them in 1988:
http://www.kentuckyconnect.com/heraldleader/news/092400/techdocs/24Tech-Mirrors.htm
I guess technology marches on.Here’s a link to what was available in the late 50’s and early 60’s:
http://www.ifrance.com/c-i-f/mirormatic.htm
And here’s a link to a description of the latest improvement on electrochromic mirrors, SPD(suspended particle device)mirrors:
http://www.refr-spd.com/press37.html