Speaker 1: Welcome to brain Stuff, production of I Heart Radio. Hey
Speaker 1: brain Stuff, I'm Lauren boge Obam and this is another
Speaker 1: classic episode from our erstwhile host, Christian Sager. Today's topic
Speaker 1: features a bit of everyday science, well every day for
Speaker 1: anyone who drives. What do those tabs on rear view
Speaker 1: mirrors actually do? Hey, I'm Christian Sager and welcome to
Speaker 1: brain Stuff. If you have a car, then chances are
Speaker 1: you also have a rear view mirror. So imagine that
Speaker 1: one night you're driving home when some joker rolls up
Speaker 1: behind you with his high beams on, blinding you. Luckily,
Speaker 1: you're able to flip the tab on your rear view
Speaker 1: and make the mirror glare resistant, eliminating most of the light.
Speaker 1: But what's going on there? How can the same piece
Speaker 1: of glass have two different amounts of reflection? This mirror's
Speaker 1: looks can be deceiving. See, your rear view isn't just
Speaker 1: one mirror, and it isn't flat. Instead, it's built in
Speaker 1: what's called a prismatic edge shape, and it contains two
Speaker 1: reflective surfaces. There's a regular shiny mirror in the back
Speaker 1: and there's a thin glass wedge right in front of
Speaker 1: it closer to the driver. The front glass surface is
Speaker 1: at an angle to the back surface. If you were
Speaker 1: to look at this mirror outside of its casing, it
Speaker 1: would be wedge shaped with the thicker edge up at
Speaker 1: the top. During a daytime drive, the angled glass surface
Speaker 1: is pointing down and you're observing the reflection of the
Speaker 1: main mirror. But when you flip that little tab, the
Speaker 1: back mirrord surface usually points towards the dark ceiling, you
Speaker 1: don't see that image. What you see instead is the
Speaker 1: image reflecting off the front of the glass. The glass
Speaker 1: only reflects about four percent of the light hitting the mirror,
Speaker 1: so it doesn't hurt your eyes. To prove that this
Speaker 1: is what's happening, take a flashlight with you one night
Speaker 1: and play with your mirror. Now, not while you're driving,
Speaker 1: but you know, while you stopped. Flip the mirror into
Speaker 1: glare resistant mode and shine the light at the ceiling
Speaker 1: or sometimes try the floor. The fully reflected image will
Speaker 1: overwhelm the front surface reflections, so you can see the ceiling.
Speaker 1: This is just the mechanism behind the basic rear view mirror.
Speaker 1: More high end mirrors may have auto dimming electrochromic technology,
Speaker 1: which uses a low voltage power supply to tint the glass,
Speaker 1: or you might even drive a car with a rear
Speaker 1: view camera system. Today's episode was written by Christian and
Speaker 1: produced by Tyler Clang. Brain Stuff is a production of
Speaker 1: iHeart Radio's How Stuff Works from Oneness and lots of
Speaker 1: other topics with more than one angle, visit our home
Speaker 1: planet how stuff Works dot com. Plus for more podcasts
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Speaker 1: or wherever you listen to your favorite shows.