Any science textbook will tell you that humans cannot see infrared light, but researchers have found that under certain conditions our eyes can actually detect the ‘invisible’ light.
Like X-rays and radio waves, infrared light waves are outside the visual spectrum.
Using cells from the retinas of mice and people, and powerful lasers that emit pulses of infrared light, the researchers found that when laser light pulses rapidly, light-sensing cells in the retina sometimes get a double hit of infrared energy.
When that happens, the eye is able to detect light that falls outside the visible spectrum.
“We’re using what we learned in these experiments to try to develop a new tool that would allow physicians to not only examine the eye but also to stimulate specific parts of the retina to determine whether it’s functioning properly,” said senior investigator Vladimir J Kefalov, associate professor of ophthalmology and visual sciences at Washington University.
The study was initiated after scientists reported seeing occasional flashes of green light while working with an infrared laser.
Unlike the laser pointers used in lecture halls or as toys, the powerful infrared laser the scientists worked with emits light waves thought to be invisible to the human eye.
“They were able to see the laser light, which was outside of the normal visible range, and we really wanted to figure out how they were able to sense light that was supposed to be invisible,” said Frans Vinberg, one of the study’s lead authors.
Researchers examined the scientific literature and revisited reports of people seeing infrared light.
They repeated previous experiments in which infrared light had been seen, and they analysed such light from several lasers to see what they could learn about how and why it sometimes is visible.
“We experimented with laser pulses of different durations that delivered the same total number of photons, and we found that the shorter the pulse, the more likely it was a person could see it,” Vinberg said.
“Although the length of time between pulses was so short that it couldn’t be noticed by the naked eye, the existence of those pulses was very important in allowing people to see this invisible light,” Vinberg added.
The human eye is a more complex and mysterious thing than we thought. Recently, a group of scientists were puzzled by flashes of green light they saw from an infrared laser, whose light should have been far outside the visible spectrum. Like scientists do, they investigated. Human eyes do indeed perceive infrared light, they found, but not they same way they perceive ordinary colors. It's weirder than that.
Their study, published this week in the journal PNAS, suggests it has to do with photons of infrared light doubling up. Infrared light has less energy than red, blue, green, or any color we consider in the visible spectrum, so it can't excite the photoreceptors in our eyes. But if two photons of infrared light hit the same receptor one right after another, their energies add up to one photon of visible light. Hence, the "green" from an infrared laser.
Fancy two-photon microscopes actually work on the same basic idea. Two photons of infrared light together excite a fluorescent molecule in a sample, causing it to glow. Infrared light has the advantage of penetrating deeper into a solid sample, so the resulting image is much clearer than you'd get with an ordinary microscope. We figured out how to make two photons work together in lab equipment before we figured out it may literally be happening in our eyes.
But right, this isn't exactly night vision—all it really works on are the focused beams of a laser. Eye doctors are interested in it as a new way to probe photoreceptors in the eye. And biohackers who are trying to modify their vision to see infrared, well, they have some more information to work with.
Perhaps most fascinating of all, though, is that this demonstrates how human vision is our hyperconstructed interpretation of reality. It's easy to believe that our eyes perceive the world as it really is, but nope. Just look at how optical illusions fool us. The same color appears different on different backgrounds, lines appear to move on their own, etc etc. Our visual system is constantly trying to find patterns in the photons streaming into our eyes—we see its interpretation of the world, not the world as it really is.
The findings are published in the journal PNAS.
Like X-rays and radio waves, infrared light waves are outside the visual spectrum.
Using cells from the retinas of mice and people, and powerful lasers that emit pulses of infrared light, the researchers found that when laser light pulses rapidly, light-sensing cells in the retina sometimes get a double hit of infrared energy.
When that happens, the eye is able to detect light that falls outside the visible spectrum.
“We’re using what we learned in these experiments to try to develop a new tool that would allow physicians to not only examine the eye but also to stimulate specific parts of the retina to determine whether it’s functioning properly,” said senior investigator Vladimir J Kefalov, associate professor of ophthalmology and visual sciences at Washington University.
The study was initiated after scientists reported seeing occasional flashes of green light while working with an infrared laser.
Unlike the laser pointers used in lecture halls or as toys, the powerful infrared laser the scientists worked with emits light waves thought to be invisible to the human eye.
“They were able to see the laser light, which was outside of the normal visible range, and we really wanted to figure out how they were able to sense light that was supposed to be invisible,” said Frans Vinberg, one of the study’s lead authors.
Researchers examined the scientific literature and revisited reports of people seeing infrared light.
They repeated previous experiments in which infrared light had been seen, and they analysed such light from several lasers to see what they could learn about how and why it sometimes is visible.
“We experimented with laser pulses of different durations that delivered the same total number of photons, and we found that the shorter the pulse, the more likely it was a person could see it,” Vinberg said.
“Although the length of time between pulses was so short that it couldn’t be noticed by the naked eye, the existence of those pulses was very important in allowing people to see this invisible light,” Vinberg added.
The human eye is a more complex and mysterious thing than we thought. Recently, a group of scientists were puzzled by flashes of green light they saw from an infrared laser, whose light should have been far outside the visible spectrum. Like scientists do, they investigated. Human eyes do indeed perceive infrared light, they found, but not they same way they perceive ordinary colors. It's weirder than that.
Their study, published this week in the journal PNAS, suggests it has to do with photons of infrared light doubling up. Infrared light has less energy than red, blue, green, or any color we consider in the visible spectrum, so it can't excite the photoreceptors in our eyes. But if two photons of infrared light hit the same receptor one right after another, their energies add up to one photon of visible light. Hence, the "green" from an infrared laser.
Fancy two-photon microscopes actually work on the same basic idea. Two photons of infrared light together excite a fluorescent molecule in a sample, causing it to glow. Infrared light has the advantage of penetrating deeper into a solid sample, so the resulting image is much clearer than you'd get with an ordinary microscope. We figured out how to make two photons work together in lab equipment before we figured out it may literally be happening in our eyes.
But right, this isn't exactly night vision—all it really works on are the focused beams of a laser. Eye doctors are interested in it as a new way to probe photoreceptors in the eye. And biohackers who are trying to modify their vision to see infrared, well, they have some more information to work with.
Perhaps most fascinating of all, though, is that this demonstrates how human vision is our hyperconstructed interpretation of reality. It's easy to believe that our eyes perceive the world as it really is, but nope. Just look at how optical illusions fool us. The same color appears different on different backgrounds, lines appear to move on their own, etc etc. Our visual system is constantly trying to find patterns in the photons streaming into our eyes—we see its interpretation of the world, not the world as it really is.
The findings are published in the journal PNAS.
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