Bites of Curiosity

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For all the emphasis we place on color, humans perceive a pretty limited range of the light spectrum. We know that “light waves occur along an electromagnetic spectrum according to their wavelengths and energy.”¹When these waves hit our retinas, specialized photoceptor cells convert this light into electrical signals sent along our optic nerves to our brains. Our brains then translate those signals into our visual understanding of the world.

The visible light spectrum for humans is roughly 390nm (nanometers) to 700nm.² We perceive the former as violet and the latter as red. But other species can perceive much more of the electromagnetic spectrum, sensing longer wavelength light, like ultraviolet rays, and higher wavelength light, like infrared rays. Many blood-sucking animals, like vampire bats and bed bugs, rely on infrared light to home in on their prey. Mosquitos are perhaps the most notorious infrared-sensing species. New studies suggest that they find hosts by detecting changes in carbon dioxide levels and then target their prey using infrared vision.³

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On the opposite side of the spectrum, in terms of both light sensitivity and size, are reindeer. They are one the few mammals that can see ultraviolet light. This likely is an adaptation related to their arctic environment, as snow reflects up to 90% of UV light. When researchers used a UV-sensitive camera to study the reindeer’s environment, they found that many things within this environment absorb ultraviolet light.⁴ Lichen, a popular food source, absorbs UV light. So too does urine and fur - common signs of predators. Appearing dark against the light-reflecting surface of the snow, the ultraviolet-sensitive eyes of reindeer can easily discern these objects in their environment, helping them more readily identify signs of danger and more easily find sustenance.

Some species can also perceive polarized light (light that is vibrating on the same plane), which we only perceive as glare unless we use specialized lenses. Many butterflies rely on polarized light to attract and identify potential mates, including the common bluebottle butterfly. While its name may sound mundane, this butterfly from the Australasia region boasts an impressive 15 different types of photoreceptor cells.⁵

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In contrast, humans have two broad types of photoreceptors (a number that sounds downright measly in comparison), rods and cones. Rods help us see in low-light conditions and grayscale, and cones help us see color. We have rods, which help us see in low-light conditions and grayscale, and cones, which help us see color. Our cones are sensitive to three types of light: red (accounting for roughly 60% of our 6 million cones), green (30%), and blue (10%).⁶The common bluebottle butterfly has cells that are analogous to rods and cones. Scientists are still unraveling the sensitivities of their photoreceptors but know they can see ultraviolet light and polarized light. They believe these butterflies have also developed vision sensitivity to slight variations in color that may be related to mating.⁵

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Studying other species’ vision and light perceiving capabilities can help us develop new technology. By replicating the visual data points of some animals, we may be able to produce cameras that are more sensitive and better able to perform in unusual conditions, perhaps giving us the tools we need to better understand the colorful world around us.