What is the purpose of the black dot on the rearview mirror in a car?
There's usually a small black dot on the edge of the rearview mirror inside a car, and not many people know what it's for.
Modern cars are often equipped with many technologies and features by the manufacturer. One of these is the small black dot on the top edge or the button on the bottom edge of the rearview mirror inside the car.
This is a detail of the automatic anti-glare system for the rearview mirror installed inside the car.
This feature is designed by car manufacturers to assist drivers in situations where glare from vehicles behind can blind them. Accordingly, vehicles equipped with anti-glare rearview mirrors will have two light sensors. The first is installed on the back of the mirror to automatically detect lighting conditions in darkness or at night.
The front sensor—typically designed as a small black dot on the top edge of the mirror—measures the amount of light emitted from behind the car, such as the headlights of vehicles behind, and then adjusts the intensity of the light on the rearview mirror accordingly to aid the driver's visibility.
Additionally, some types of automatic anti-glare rearview mirrors commonly found on Japanese car models have a button on the lower edge of the rearview mirror to activate the automatic anti-glare feature.
For car models that typically have interior rearview mirrors but lack an automatic anti-glare feature (commonly found in mainstream models), manufacturers design a small lever on the back of the mirror. When blinded by the headlights of vehicles behind or by ambient light conditions, the driver simply flips the lever down and adjusts the mirror's angle to suit their viewing needs.