Understanding How Auto-Dimming Rearview Mirrors Function Your vehicle may very well have an automatically-dimming rearview mirror, but do you really understand how this technology works? Designed to dim out that annoying glare that comes from having a vehicle behind you when the sun goes down, your mirror contains a special mirror design that prevents you from having to switch between normal view and anti-glare view. Your mirror is constructed using two different pieces of glass. In between these pieces, there is a special electrochromic gel that allows a low-voltage amount of electricity to pass through. When your mirror senses that there is some degree of glare present behind your vehicle, the mirror will begin to dim in order to prevent this glare. Most manufacturers provide you with the ability to turn this auto-dimming feature if you don’t want to use it. In general, it’s a very convenient safety feature to have.