Welcome to brain Stuff, production of I Heart Radio. Hey brain Stuff, I'm Lauren boge Obam and this is another classic episode from our erstwhile host, Christian Sager. Today's topic features a bit of everyday science, well every day for anyone who drives. What do those tabs on rear view mirrors actually do? Hey, I'm Christian Sager and welcome to brain Stuff. If you have a car, then chances are
you also have a rear view mirror. So imagine that one night you're driving home when some joker rolls up behind you with his high beams on, blinding you. Luckily, you're able to flip the tab on your rear view and make the mirror glare resistant, eliminating most of the light. But what's going on there? How can the same piece of glass have two different amounts of reflection? This mirror's looks can be deceiving. See, your rear view isn't just
one mirror, and it isn't flat. Instead, it's built in what's called a prismatic edge shape, and it contains two reflective surfaces. There's a regular shiny mirror in the back and there's a thin glass wedge right in front of it closer to the driver. The front glass surface is at an angle to the back surface. If you were to look at this mirror outside of its casing, it would be wedge shaped with the thicker edge up at
the top. During a daytime drive, the angled glass surface is pointing down and you're observing the reflection of the main mirror. But when you flip that little tab, the back mirrord surface usually points towards the dark ceiling, you don't see that image. What you see instead is the image reflecting off the front of the glass. The glass only reflects about four percent of the light hitting the mirror,
so it doesn't hurt your eyes. To prove that this is what's happening, take a flashlight with you one night and play with your mirror. Now, not while you're driving, but you know, while you stopped. Flip the mirror into glare resistant mode and shine the light at the ceiling or sometimes try the floor. The fully reflected image will overwhelm the front surface reflections, so you can see the ceiling. This is just the mechanism behind the basic rear view mirror.
More high end mirrors may have auto dimming electrochromic technology, which uses a low voltage power supply to tint the glass, or you might even drive a car with a rear view camera system. Today's episode was written by Christian and produced by Tyler Clang. Brain Stuff is a production of iHeart Radio's How Stuff Works from Oneness and lots of other topics with more than one angle, visit our home
planet how stuff Works dot com. Plus for more podcasts for my heart Radio, visit the iHeart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.