The shape that changed our world forever

did you know that stop signs used to be yellow back in the 1920s even though red had already become known for stop in traffic lights the convention in science wasn't yet established and there were two major problems with red one there wasn't yet a way to make red pigment that wouldn't fade and two red is way harder to see at night you see your eye has three types of cones that detect color red green and blue cones but at night there isn't enough light to activate these cones in your retina and so your eyes rely on rods which are much better at perceiving low light and if we look at the wavelength sensitivity of rods you'll notice they actually don't even pick up red wavelengths when we see red at night it can only be picked up by cones and as a result red is the hardest color to see in low light so while a traffic light shining right is one thing a lowly lit red sign is completely different on top of this even in daylight our eyes are actually most sensitive to a yellow greenish color this is because it's right in the overlap between our red and green cone sensitivity peaking at about 550 nanometers making it a perfect option for visibility but not exactly one for consistency with red meaning stop so when did the switch to red signs happen and how did we overcome this hurdle it's actually one of the most ingenious and coolest inventions to ever come about retro reflection [Music] i'm here at 3m's innovation theater the home of the retro reflector where it was invented created and first implemented and we're going to talk about what they are and how they work i have a little laser light here but to not blind you we understand if a light comes into the mirror it's going to reflect back into this lens or your eye but if you point a laser at an angle to a mirror it exits at the equal angle the other way so you can see over there i have that laser pointer on the shelf and that's not very useful if you're trying to get light reflecting back to someone on a sign so we need a better solution and 3m came up with that many decades ago they first used these glass beads now when light enters glass it's a different refractive index so it actually bends the light if we put this down here the white surface that's reflective behind it and i shine this laser through it you can see that laser comes back to me now instead of bouncing out the other direction it's actually shooting back at my stomach a little faint but still there but 3m took that principle even further with a full cube retro reflector if we take this and just talk about these first two mirrors here if i shine a laser in one side of that mirror it will bounce out at the equal and opposite angle and then do it again and you can see on me this laser looks basically just as strong as it did going in as it does on me so that's really useful that it's reflecting back to the source where it's coming from and when you think about signage you want the light to hit it even if it's at a weird angle and come back to you so you can see the thing by adding a third mirror down here we can now basically point anywhere on here and we're gonna have reflection that ends up back towards me you can see it here as well even though i'm pointing on the bottom and that is a basic 101 of how a retro reflector works now the question is how do we go from the principle of retro reflection to getting it on a huge variety of surfaces like not only signs but multiple plastics the lines on the road and even clothing walk me through what the heck you are moving around here these are our reflective sheeting what we have here are different type of reflective sheeting so these are all basically full of retro reflectors right correct and this is full of retro reflectors basically each of these little squares has 6 000 retroflectors per square centimeter yes you did your homework that's pretty good so you got it this though is like a metal backing of which these retro-reflective sheets are put onto totally correct the most important sign of the role the stop signs with our materials i wasn't about to leave 3m without a sign of my own so i made sure to ask specifically how the signs get put together we're going to start with the retroflective cheating so it'll cut its size and our retroflective sheeting is basically a big sticker so there's a liner and adhesive on the back so once you apply it on here you get kind of this lip this overhang so we have to trim that off and then separately we'll take the electrocut overlay film or e-conf as some people call it and we'll put it through a friction-fed platter we wrote asap science yes i hope i got to keep this you just kind of grab the edge and just push it and then you can just lift the letter off whoa okay there we go all right some letters like the a will actually have a little floating piece right like the middle and so applying this pre-space allows you to keep everything in place and remove the liner and essentially you end up with something like this so you remove the liner the green is stuck to the white retro reflective sheeting it's on aluminum and the last thing to do is to remove this pre-space which you want to give it i would love to are you ready oops wow look at that asap science almost every street name sign is made like this before digital printing that's crazy and another way to manufacture science is using digital printing so digital printing's been around for about 10-15 years probably at 3m so this is printing on retro-reflective sheeting exactly this specific printer uses hp latex inks so it's water-based so it's similar to like your printer at home where it's just laying down ink all right can we see a little something something absolutely it's maurice i'm science science that's so cool okay we're outside in the dark and we're gonna do a little experiment with the sign now to see it in action so if i shine this flashlight on the ground my immediate surroundings are pretty visible but become increasingly less visible as you go further out and that's because light scatters in all directions and less photons are actually making it back to the camera lens but if i shine this light now over towards greg holding our fancy retro reflectoring sign and put the light right beside the camera lens you'll see just how much brighter the sign is than almost anything else the light is touching even though it's all the way over there now of course if i move the light away from the lens the sign becomes less bright even here i'm about six inches go a little further about a foot you can see how much darker the sign is and that's because the camera lens or you are no longer the source and instead the majority of the light is bouncing back over here over here where i'm holding the light i see the sign just as bright but you don't and that's because the light is always reflecting back to the source you've likely seen this while driving at night when there are minimal overhead lights signs super far in the distance are extremely bright while things closer are completely dark even the metal post seems invisible here now what about when it's raining outside sure in the broad daylight you can still see the lines on the road but i think we're all familiar with that scary problem of lines disappearing at night the problem here is that the water actually changes the refraction of light so where the retro reflectors act ideally under dry conditions as soon as water is on top of them their refractive index is lowered by a ratio of 1.33 and so the light leaves at a different angle sending less back to the source and this is incredibly important because while only 25 percent of driving occurs at night 55 of deaths from car accidents happen when it's dark with rain being disproportionately dangerous at low light conditions compared to the day to combat this rain visibility problem 3m actually developed these elements which are retro reflectors that have different refractive indices so on this side we have elements to have a refractive index of 1.9 and they work well in dry conditions and on this side we have elements that have a 2.4 refractive index and work better in wet conditions and on top they're both in air and on the bottom they're both submerged in water and i'm going to show you what happens when we're in the dark and shine a light on both of these you can see that the one on the left at the top is optimized for dry conditions because it's flashing back more light and then the one at the bottom on the right is optimized for water and is sending more light back to us even though it's submerged in water now of course the best solution is to include a mix of these elements in the product whether it's the layer put on top of painted lines or directly into taped lines so that people can see them in either weather condition if it's dry the 1.9 will send the light back while the 2.4 won't and when it's wet the opposite occurs so behind me we have a variety of painted lines some have the regular glass beads on them and other ones have the 3m elements on them with the 1.9 refractive index or the 2.4 refractive index or a combination of those and we're going to see what happens in the dark when they get rained on here's the setup in the dark before the rain machine has been turned on and you can see all the lines are equally visible but as the rain begins to run some of the lines slowly start to become obscured and harder and harder to see it's only the few stripes on this right hand side that remain visible as they have varying amounts of the water reflective elements and here's the difference in the real world on the left is a wet line without water reflective elements and on the right you can see it with these elements and as a result you can actually see that line even in the rain so there you have it road signs are officially way cooler than you probably thought or at least are a lot cooler than i ever realized they were before making this video and hopefully i've convinced you of that too i want to send a huge thank you to 3m for having me at the facility and to jc and gus for showing me around and teaching me and especially making me multiple signs that i could bring home back here to the asap science headquarters i will cherish it forever thank you so much for watching make sure you like the video subscribe if you haven't already and we'll see you next time for some more science peace

Channel: AsapSCIENCE

Views: 847,263

Keywords: asapscience, asap science, asapscience youtube, asap science youtube, asap, science, fun science, retroreflection

Id: 4iY8JqHN-kI

Length: 9min 36sec (576 seconds)

Published: Thu Aug 11 2022