What Do Those Tabs On Rearview Mirrors Actually Do?


(classical music)
(writing on chalkboard) – Hey there, I’m Josh Clark,
and this is the Brain Stuff where I explain rear view mirrors to you. Have you you ever been
driving along at night and all of a sudden some
piece of human garbage drives up behind you with his brights on and just rides you, and you’re like, what’s goin’ on, what
is your problem buddy? And then you remember, oh
yeah, I’ve got a little tab on my rear view mirror
that makes magic happen. You flip the tab and all of a sudden, you send that guy packin’. Sure here’s still behind
you, but it’s not a problem any longer, especially if you
can kind of angle yourself so you don’t get your side
view mirrors in your face. You’re just in heaven basically, goin’ down the road with that guy. And who cares about him
and all of his problems and what is his day was like? But have you ever wondered, like, what just happened when
I flipped that tab? Well, I’m here to explain it to you. See, what looks like a little piece of flat mirror hanging from your windshield is actually something that’s
called prismatic wedge. What looks to be flat is actually a angled mirror with a wedge of glass, it’s just normal, see-through, flat glass, in front of it, at an angle. So when you’re driving
along and it’s normal daylight hours and
everything’s just typical, when you look into the mirror,
you’re actually looking right through that angled glass in front, which is now downward,
to the mirror in back. And again, everything’s normal, you’re looking into a
mirror, what’s there to say? But when it’s nighttime,
and somebody drives up on you with their brights
and you flip that tab, the roles are reversed. The mirror in back is now angled upward, and the glass is flat to you, which means that about 4% of the light is actually being reflected,
which dims the image. Presto! And if you’re one of
those suspicious types who doesn’t take guys and
YouTube’s word for it, you can go out and prove it to yourself. Get this, get into a parked
car, preferably yours, in park, with the keys
out of the ignition, at night, with a flashlight. Those five factors are very important. Put the mirror in dim mode
and turn the flashlight on so it’s pointed at the ceiling. What you’re gonna see is a
full reflection of the ceiling because the light on the
ceiling from the flashlight is so bright, it overwhelms
that measly 4% reflection of what’s behind you in the glass. It’s been proven, try it, I dare you. Now, there are some fancy
schmancy new mirrors that use electrochromic technology that employs a low
voltage electrical current go through the glass and
actually physical tint it, that’s a whole other
can of worms altogether. All I’m talkin’ about
is that magic, normal, old-timey tab rear view
mirror that does some pretty cool stuff, considering how
easily you take it for granted. So go forth, and apologize
to your rear view mirror for taking it for granted. Say, I understand you now, I get you, I feel closer to you. And if you don’t have
one, maybe either get a new car that does have
one, or you can go to your local auto parts store and pick one up. Do it today.

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