outside day/night rear view mirror

This is the way it would work,, you know the inside mirror that can dim the lights from behind, this would work on thsame principle, only it would be incorported into the outside mirror. say someone is coming up from behind and they don't realize their lights are on high beam, an blinding you not to mention possibly making you mad, there would be a sensor inside the mirror that would automatically make the mirror act as the inside day/night mirror does and instead of manually having to furn the lights brightness down, it would do it automatically.