1. A forward-facing sensor recognizes low ambient light levels and signals the mirror to begin looking for glare. A: 2. A rearward-facing sensor then detects glare from the vehicles traveling behind you, sending voltage to the mirror's EC gel in proportion to the amount of glare detected. A: 3. The mirror dims in proportion to the glare and then clears when the glare is no longer detected. A: 4. The interior mirror's sensors and electronics control the dimming of the mirrors.