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You've seen those viral videos of colorblind people putting on special glasses and reacting to colors they've never seen before! Today, we'll explore how colorblindness works and what those glasses try to do to fix it!

Hosted by: Hank Green
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Sources:
https://nei.nih.gov/health/color_blindness/facts_about
http://cen.acs.org/articles/95/i6/Experimenting-EnChromas-color-blind-assistance.html
http://www.smithsonianmag.com/innovation/scientist-accidentally-developed-sunglasses-that-could-correct-color-blindness-180954456/?no-ist
https://pogue.blogs.nytimes.com/2013/08/15/glasses-that-solve-colorblindness-for-a-big-price-tag/?_r=1
https://www.ncbi.nlm.nih.gov/pubmed/6971497
www.dtic.mil/get-tr-doc/pdf?AD=ADA093031
http://faculty.washington.edu/sbuck/545ColorClass/Sharpe%26Jagle.2001.pdf
http://www.sciencedirect.com/science/article/pii/S003962578180001X
http://faculty.washington.edu/sbuck/545ColorClass/Sharpe%26Jagle.2001.pdf
https://www.microsoft.com/en-us/garage/profiles/color-binoculars/

Images:
https://commons.wikimedia.org/wiki/File:Cone-fundamentals-with-srgb-spectrum.svg
https://commons.wikimedia.org/wiki/File:%D0%92%D0%B5%D1%87%D1%96%D1%80_%D0%BD%D0%B0_%22%D1%96%D0%BD%D1%82%D0%B5%D0%B3%D1%80%D0%B0%D0%BB%D1%96%22_-_%D1%80%D1%96%D1%87%D0%BA%D0%B0_%D0%9F%D1%96%D0%B2%D0%B4%D0%B5%D0%BD%D0%BD%D0%B8%D0%B9_%D0%91%D1%83%D0%B3.jpg
https://commons.wikimedia.org/wiki/File:Deuteranopia_sight.jpg
https://commons.wikimedia.org/wiki/File:Ishihara_9.png
A while back, there were a whole bunch of videos with the same theme that went viral: someone who is colorblind puts on special glasses, and suddenly they can see the world in all its colorful glory!

Some people freak out, some people cry, some people can't stop staring at colors they say they've never seen. When we first heard about this, we were like we need to make a video about that immediately!

And then we spend years basically, trying to get to the bottom of it. And this is the culmination of that. Thank you, to our writing staff.

But the glasses don’t just, like, turn on a bunch of new colors for colorblind people. And when people put the glasses on, they aren’t suddenly seeing the world the way people with normal color vision do. The glasses just filter light in a way that makes it easier for people with certain types of colorblindness to tell the difference between colors.

If someone’s colorblind, that means something’s up with the cones in their eyes — the photoreceptors that detect color. There are three types of cones: for seeing short, medium and long wavelengths, which roughly correspond to blue, green, and red. There are lots of different types of colorblindness, and in almost all of them, people can see at least some colors.

The exception is monochromacy, where people don’t have any cones at all and they see the world in black, white, and grey. But that is incredibly rare — only about 1 in 30,000 people have it. There’s also dichromacy, where one type of cone is missing.

Where someone is missing all of their green cones, for example, they see the world in just blues and yellows. But it's a lot more common to have what’s known as anomalous trichromacy: where you have all three cones, but one type gets activated by the wrong wavelengths. About 6.3% of men, and 0.37% of women, have anomalous trichromacy.

And in the vast majority of those people, it’s their red or green cones that are affected, which is why most colorblind people confuse green and red. In deuteranomaly, the green cones detect wavelengths that are too high — so, on the redder end of the spectrum. Red light activates both red and green cones, which the brain interprets as a kind of yellowish color.

Protanomaly is kind of the opposite: the red cones detect wavelengths that are too low, so green light can activate the red cones. Either way, the red and green cones are activated by similar wavelengths, so there’s confusion around red and green, which can both look yellowish. Like, it might be kind of hard to tell the difference between a lemon and a lime, or between red and green peppers.

But there are a couple of ways to help colorblind people tell the difference between colors, even without fancy glasses. Like with an app that changes the colors for you. If you were trying to figure out which peppers were the red ones, you could pull out your phone and hold the camera up to them, and the app would detect the red peppers and change them to a color that would be easier to distinguish, like pink.

Some apps and video games have settings that’ll do something similar — so you don’t confuse the enemies outlined in red with the people on your team outlined in green, for example. There are also colorblind-friendly contact lenses. You wear a special contact lens in just one eye, which is usually tinted deep red so it blocks out a lot of green light.

Green objects will look much darker through the tinted lens, so by comparing what you see with each eye, it’s easier to tell the difference between green and red. These lenses can help you pass tests for colorblindness, like the ones where you check which number you see in different-colored dots, and it can also help people in some specific jobs, like electricians. You don’t want to get the wires wrong, when you’re an electrician.

Some people who’ve used these lenses say that they do start to see green and red differently. But they don’t really correct color vision. The glasses that spawned all those viral videos, on the other hand, do try to correct color vision.

They’re designed to solve the problem of the cones overlapping, so colors don’t activate the wrong cones. They only work for the types of red-green color blindness where you have all three cones, though — so either deuteranomaly or protanomaly. The key is to block the specific wavelengths that are causing the most confusion — so the wavelengths of red and green that trigger both the red and green cones.

The glasses use what’s known as multi-notch filtering, where they’re embedded with rare earth metals that absorb certain wavelengths of light, leaving just the wavelengths that a colorblind person’s eyes have an easier time distinguishing. So red things will be more red, and green things will be more green, making it easier to distinguish between them. That's also what happens if someone with regular vision wears the glasses — they’ll see the primary colors of light much more vividly.

But for colorblind people, the glasses will only work if their colorblindness isn't too severe. If their cones overlap too much, there's not much these glasses can do, because they won’t block all the wavelengths that trigger both types of cones. On the other hand, some of the people that the glasses do work for say that they can see colors they never have before — like certain shades of purple.

People with normal color vision see purple when there’s a mix of red and blue wavelengths reaching their eyes. But with deuteranomaly, part of the red light activates the green cones, which muddies the color. It’s possible that with the glasses blocking the wavelengths of light that activate the green cones, people can see shades of purple they wouldn’t otherwise be able to see.

Of course, the glasses can not cure color blindness, because nothing has physically changed about your eyes or your cones. But for the people in those viral videos, the world really does look different — though I was skeptical of that at first. Although, it does not look exactly the same as the way people with normal color vision see it.

Thanks for watching this episode of SciShow! If you’re interested in learning more about the science of vision, check out our video on why so many people need glasses these days — aka the nearsightedness epidemic.