Clever light-sensing technology allows mirrors in some modern cars to dim at night to avoid bright headlights behind from dazzling you. There is a sensor at the back of the interior mirror, it can sense darkness outside when it’s close to night time (or a dark tunnel etc). There is another sensor at the front of the mirror inside or close to the glass which sense how bright headlights behind you are. The anti-dazzle function of the mirror will automatically start working if needed. In some cars this will also dim the door mirrors.

If your mirror doesn’t automatically dim, then dim it with this lever.