But some people can, thanks to certain genes or conditions.
Thanks to Brilliant for supporting this SciShow video! As a SciShow viewer, you can keep building your STEM skills with a 30-day free trial and 20% off an annual premium subscription.
Believe it or not, there are people who can see what’s invisible to most of us. I’m not talking about some sci-fi superpower like X-ray vision, but how it actually works isn’t all that far off. The average person sees millions of colors from violet to red, but those colors don’t make up all of the light there is. Because of the structure of our eyes, there are some wavelengths of light outside of the range that triggers our vision, making them impossible to see. Not for everyone, though! Thanks to certain genes or conditions, some people can see what’s invisible to the rest of us.
When light bounces off an object and enters our eye, it passes through the cornea first. That’s the outer, dome-shaped structure that bends light toward the center of the eye. Some of this light goes through the pupil, which gets bigger or smaller in different settings to let in more or less light. Then this light passes through the lens, a part of the inner eye that helps focus it further. Finally, the light hits the retina at the back of the eye: a layer of tissue covered with special cells called photoreceptors. Now, our photoreceptors can only respond to certain wavelengths of light, which for humans, is between 380 nanometers and about 700 nanometers.
Light waves can have many different wavelengths, and those wavelengths make up the spectrum of visible light that we can see. Outside of the visible spectrum of light, there’s a whole realm of ultraviolet, X-rays, and gamma ray radiation. But as cool as it would be to have X-ray vision or see UV light like a bee, it’s actually a good thing we don’t, because UV light can be just as damaging to our eyes as it is to our skin. Which is why there are barriers to that light getting too deep into our eyeballs, mostly within the lens, which has yellowish pigments that absorb UV rays before they go any further.
But some people are missing a lens in one or both of their eyes, so that UV doesn’t get blocked. Lacking a lens is called aphakia. And in aphakic people’s eyes, UV light can sail straight through the eye and trigger the photoreceptors on the retina. Individuals with this condition have said that UV light looks whitish-blue or -violet to them. One of the most famous people with aphakia was the artist Claude Monet, who had the lens of one eye removed as a treatment for cataracts.
So the colors of light that appear bluish-violet to us have very short wavelengths, and UV’s wavelength is even shorter than those, so we can’t see it. But some people can, thanks to certain genes or conditions. org.
On the other end of the spectrum, red light has the longest wavelengths that are considered visible. Wavelengths longer than 800 nanometers are what we call infrared, and are generally undetectable to the naked eye due to the lack of energy. However, some scientists reported that they could see some infrared in lab experiments throughout the 20th century. In 2014, a group of scientists shined pulses of infrared laser light into volunteers’ eyes and all of them were able to detect a visible light signal. The color they saw corresponded with a wave frequency that was about double the frequency of the laser, which suggested that when the laser was pulsing quickly, the photoreceptors in the eye would process two pulses of infrared light at once, essentially tricking it into going off.
We have established that there are ways to see light beyond either end of the visible spectrum. There are also people who can see extra colors within the spectrum. This is due to two kinds of photoreceptors in our eyes: rods, and cones. Most humans have three different types of cones, and each one contains different pigment molecules that absorb light. Depending on which pigments it contains, each cone is most sensitive to a different wavelength of light: either blue, green, or red. However, in rare cases, these four types of cones are triggered by four different colors of light and produce millions of colors that can’t be made with just three cones. This condition is called tetrachromats, and it allows people to see a whole range of colors and shades that are completely indistinguishable to most of us.
This is a reminder that what any one person sees isn’t an objective representation of the world. It’s just a window into the world, and quirks of physics and biology can reshape that window and redefine what we consider visible. It’s all about perspective! Yes, it’s supported by amazing people like you who continue to watch SciShow videos, but it’s also supported by the interactive online learning platform with thousands of lessons to choose from in math, science, and computer science. For example, there’s the Brilliant course: Geometry I that teaches you the ins and outs of angles. With this course’s geometry puzzles, you can learn your own way and come up with creative geometric problem-solving techniques. You might even think about this SciShow video in new ways after taking that Brilliant course. If you thought it was a feat to fit all of our rods and cones in these little eyes, just imagine the incredible geometry involved in making mantis shrimp eyes work. And after you take this Brilliant course, it’ll be a lot easier to imagine.
You can find it all at Brilliant.org/SciShow. That search will start you off with a free 30-day trial and 20% off an annual premium Brilliant subscription. Thanks for watching! [♪ OUTRO]