Why do rear view mirrors work

Both the front and rear surfaces actually are reflecting light back at you, regardless of the position. The front surface at this point is just weakly reflecting the light from the back seat of your car. You just see the dim reflections off the front glass. Another method for dimming the rear-view mirror is electrochromism, which allows for automatically adjusting the amount of light reflected by the rear-view mirror. Electrochromism is a phenomenon that allows materials to change color when different energy levels are applied to them.

Modern versions of these systems have photo-detectors mounted on them that sense the amount of light reaching the mirror. Most show the image in the infotainment screen, but some broadcast it in the rearview mirror, or in the instrument cluster.

When headlights behind you reflect off the mirror, you can adjust it — or it adjusts automatically, depending on the mirror — to reduce the glare. A manual mirror is adjusted by flipping a lever on the back or bottom of it; this is known as a prismatic mirror.

The internal mirror glass is wedge-shaped, with the thicker end at the top, and the mirrored surface at the back. At night, when headlights behind bounce off the mirror and cause that distracting glare, flipping the lever changes the angle.

The rear mirrored surface now reflects the headlights up and out of your eyes. Auto-dimming mirrors serve the same anti-glare purpose but work differently.

They use two pieces of glass that are coated with electrically-conductive material. Most of these mirrors contain two sensors. The glare sensor points to the back and determines how much light is hitting the mirror. When the glare is gone, the power switches off and the mirror brightens again. To get a wider view without going digital, automakers put a convex surface on the passenger-side exterior mirror.

The rearview mirror should show you the full view out the back window, not the rear seat, and be angled to display between the pillars on either side of the rear window. Mobile Newsletter chat subscribe. Under the Hood. How does a car's rearview mirror work when it's in the glare-resistant setting? Why does a mirror exchange left and right but not up and down? How do one-way mirrors work? Cite This! Try Our Crossword Puzzle!