The colors of the rainbow are all around us, but hues most of us can't see, including ultraviolet—a wavelength that eludes many humans but, surprisingly, can be sensed by many animals.
Ultraviolet (UV) wavelengths are shorter than those in the visible spectrum, but can people see them? The answer depends on how old you are and whether your eyes have UV-filtering lenses, experts told Live Science.
First, it is important to understand How vision works. At the back of the eye, the retina contains photoreceptors that sense light and send signals of wavelengths to the brain via the optic nerve, which interprets them as color.
In fact, our blue-detecting cones can detect some UV light. However, the lens — the clear, curved structure in the eye that focuses light on the retina and helps us see more clearly — filters out UV light, so high-energy wavelengths don't actually reach the cones. Michael's bookA biologist who studies vision at Lund University in Sweden told Live Science.
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Or at least the lens filters out most UV wavelengths for most people. Despite the lens's ability to filter out most UV light – to protect our eyes from UV damage, Age structures in the eyes and increase the risk of cancer – most young people can feel it to some extent. A small 2018 study published in the journal PLoS One, all college-age participants at the University of Georgia could see UV light at approximately 315 nanometers. (The full range of UV light ranges from about 10 to 380 nm, with violet beginning later.) During the experiment, „our subjects consistently reported that the light appeared in a nondegrading violet-blue,” the researchers wrote in the study. But this ability declines around age 30, indicating that aging reduces the ability to see UV wavelengths.
However, some people can see more of the UV light spectrum. Until the 1980s, cataract surgery involves removing the cloudy lens from the eye and replacing it with a replacement, so the operator can see ultraviolet light. For these people, and those born without a lens, the UV light is pale blue or pale purple, Bogue said. A famous example is the Impressionist painter Claude Monet After cataract surgery in 1923 he noticed more blue and purple overtones in water lilies and reflected this contrast in his later paintings.
But while most adults can't see UV light, that's not the case in the animal world. Many mammals — including dogs, cats, ferrets and reindeer — can see some ultraviolet wavelengths throughout their lives, according to a 2014 study published in the journal Nature. Proceedings of the Royal Society b. The study noted that the ability to see UV light is widespread among invertebrates, fish, birds, reptiles and amphibians, which often have cones specifically designed to detect UV light — and the lenses that allow it.
Why can so many animals see in the UV range? „Any color vision can improve contrast for detecting objects or important things in your environment,” explained Bock.
There are several ways that UV helps animals do this. For example, many predatory marine organisms use UV light to help them see the silhouettes of prey, such as plankton and fish larvae, because there is more UV light in shallow water. Thomas Cronin, a biologist studying visual ecology at the University of Maryland, Baltimore County. A lot Insects use this type of vision to perceive patterns in flowersAnd some Use polarized UV light In the sky to help them go. Many birds They signal to each other through their feathers Use it in colors and in the UV range Find ripe berries.
„The more we look at it, the more it becomes clear that it's very common,” Bogue added.
In fact, the ancestor of vertebrates could see ultraviolet light and had a specialized photoreceptor, according to a 2003 study in the journal PNAS. But somewhere in the evolutionary history of humans, that photosynthesis became more sensitive to detecting violet rather than ultraviolet wavelengths. Maybe it's because we're a long-lived species that we can't withstand the damage to our eyes, or because UV light causes blurred vision, Cronin said.
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