1 00:00:01,920 --> 00:00:06,520 Speaker 1: Welcome to brain Stuff, production of I Heart Radio. Hey 2 00:00:06,600 --> 00:00:09,160 Speaker 1: brain Stuff, I'm Lauren boge Obam and this is another 3 00:00:09,160 --> 00:00:13,000 Speaker 1: classic episode from our erstwhile host, Christian Sager. Today's topic 4 00:00:13,080 --> 00:00:15,760 Speaker 1: features a bit of everyday science, well every day for 5 00:00:15,880 --> 00:00:18,960 Speaker 1: anyone who drives. What do those tabs on rear view 6 00:00:19,000 --> 00:00:27,360 Speaker 1: mirrors actually do? Hey, I'm Christian Sager and welcome to 7 00:00:27,400 --> 00:00:30,240 Speaker 1: brain Stuff. If you have a car, then chances are 8 00:00:30,320 --> 00:00:33,000 Speaker 1: you also have a rear view mirror. So imagine that 9 00:00:33,040 --> 00:00:35,760 Speaker 1: one night you're driving home when some joker rolls up 10 00:00:35,800 --> 00:00:39,000 Speaker 1: behind you with his high beams on, blinding you. Luckily, 11 00:00:39,240 --> 00:00:41,360 Speaker 1: you're able to flip the tab on your rear view 12 00:00:41,400 --> 00:00:44,680 Speaker 1: and make the mirror glare resistant, eliminating most of the light. 13 00:00:45,000 --> 00:00:47,280 Speaker 1: But what's going on there? How can the same piece 14 00:00:47,320 --> 00:00:50,919 Speaker 1: of glass have two different amounts of reflection? This mirror's 15 00:00:51,080 --> 00:00:54,720 Speaker 1: looks can be deceiving. See, your rear view isn't just 16 00:00:54,880 --> 00:00:58,440 Speaker 1: one mirror, and it isn't flat. Instead, it's built in 17 00:00:58,480 --> 00:01:02,200 Speaker 1: what's called a prismatic edge shape, and it contains two 18 00:01:02,240 --> 00:01:05,960 Speaker 1: reflective surfaces. There's a regular shiny mirror in the back 19 00:01:06,280 --> 00:01:08,760 Speaker 1: and there's a thin glass wedge right in front of 20 00:01:08,800 --> 00:01:12,160 Speaker 1: it closer to the driver. The front glass surface is 21 00:01:12,160 --> 00:01:14,920 Speaker 1: at an angle to the back surface. If you were 22 00:01:14,959 --> 00:01:17,520 Speaker 1: to look at this mirror outside of its casing, it 23 00:01:17,560 --> 00:01:20,280 Speaker 1: would be wedge shaped with the thicker edge up at 24 00:01:20,280 --> 00:01:23,960 Speaker 1: the top. During a daytime drive, the angled glass surface 25 00:01:24,080 --> 00:01:27,399 Speaker 1: is pointing down and you're observing the reflection of the 26 00:01:27,440 --> 00:01:30,440 Speaker 1: main mirror. But when you flip that little tab, the 27 00:01:30,480 --> 00:01:34,080 Speaker 1: back mirrord surface usually points towards the dark ceiling, you 28 00:01:34,080 --> 00:01:36,800 Speaker 1: don't see that image. What you see instead is the 29 00:01:36,840 --> 00:01:40,280 Speaker 1: image reflecting off the front of the glass. The glass 30 00:01:40,319 --> 00:01:43,520 Speaker 1: only reflects about four percent of the light hitting the mirror, 31 00:01:43,680 --> 00:01:46,280 Speaker 1: so it doesn't hurt your eyes. To prove that this 32 00:01:46,360 --> 00:01:49,000 Speaker 1: is what's happening, take a flashlight with you one night 33 00:01:49,040 --> 00:01:51,960 Speaker 1: and play with your mirror. Now, not while you're driving, 34 00:01:52,040 --> 00:01:55,080 Speaker 1: but you know, while you stopped. Flip the mirror into 35 00:01:55,120 --> 00:01:58,080 Speaker 1: glare resistant mode and shine the light at the ceiling 36 00:01:58,240 --> 00:02:01,800 Speaker 1: or sometimes try the floor. The fully reflected image will 37 00:02:01,880 --> 00:02:05,320 Speaker 1: overwhelm the front surface reflections, so you can see the ceiling. 38 00:02:06,000 --> 00:02:09,400 Speaker 1: This is just the mechanism behind the basic rear view mirror. 39 00:02:09,880 --> 00:02:14,320 Speaker 1: More high end mirrors may have auto dimming electrochromic technology, 40 00:02:14,560 --> 00:02:18,079 Speaker 1: which uses a low voltage power supply to tint the glass, 41 00:02:18,639 --> 00:02:21,160 Speaker 1: or you might even drive a car with a rear 42 00:02:21,240 --> 00:02:28,200 Speaker 1: view camera system. Today's episode was written by Christian and 43 00:02:28,280 --> 00:02:30,919 Speaker 1: produced by Tyler Clang. Brain Stuff is a production of 44 00:02:30,960 --> 00:02:33,480 Speaker 1: iHeart Radio's How Stuff Works from Oneness and lots of 45 00:02:33,520 --> 00:02:35,680 Speaker 1: other topics with more than one angle, visit our home 46 00:02:35,720 --> 00:02:38,840 Speaker 1: planet how stuff Works dot com. Plus for more podcasts 47 00:02:38,880 --> 00:02:41,959 Speaker 1: for my heart Radio, visit the iHeart Radio app, Apple Podcasts, 48 00:02:42,080 --> 00:02:43,799 Speaker 1: or wherever you listen to your favorite shows.