Why Objects In Your Car's Side Mirror Are Closer Than They Appear

If you've ever driven a car or closely observed someone else driving, you know how important the side mirrors are. They give the driver a clear view of what's behind on either side, which helps in maneuvering the car safely while driving or parking. However, if you've ever looked at these mirrors closely, you may have seen a written message that reads, "Objects in mirror are closer than they appear." That's because these aren't the flat mirrors you might have in your house. They are convex mirrors.

But why do cars use convex mirrors? To understand this, you first need to know how the human eye sees things. In simpler terms, when you look at any object, the light (from the sun or a bulb) reflects off it and into your eyes, producing an image. Things like the object's shape, color, and texture affect how the light is reflected. When you look at the same object through a mirror, light from the object reflects off the mirror and into your eyes. However, if you view the object through a convex mirror (where the reflective surface bulges outward), it will appear smaller and farther away than it actually is. 

The text on a car's side mirror informs both drivers and passengers about this. These convex mirrors aren't just limited to cars. You may have also noticed them in garages, parking lots, and even shopping malls.

Cars have convex mirrors instead of flat ones because they give a wider field of view. This means there are fewer blind spots, and the driver can see what's behind the car more clearly. However, the curved surface of a convex mirror also causes lights to reflect differently, which results in objects and other cars appearing farther than they actually are. 

In the US, the law requires the driver's side mirror to be flat. This gives an accurate view of what's behind the car since the light is reflected unaltered. However, the passenger side mirror can be convex, which gives a wider field of view. This combination of flat and convex mirrors helps the driver understand the car's surroundings. Keep in mind that not every car has this combination of mirrors. For instance, in Europe, the law allows cars to have convex mirrors on both sides. 

The question of which of the two is ideal may become irrelevant once cameras fully replace traditional side mirrors. Until then, you'll have to adjust the side mirror to get the best possible view and minimize blind spots.