Blue Light Doesn’t Actually Fry Your Eyes. The Real Problem Is Much Stranger.

4 min readHere’s what you’ll learn when you read this story:Blue light myths are everywhere, so researchers decided to test how it really affects our vision.In their experiment, subjects looked at two points of light in different colors and said when the points were far enough apart to look like two, not one.Blue was the toughest to separate because its short waves scatter most, but darker eyes handled it better than lighter ones did.Myths about blue light have infiltrated the internet. It won’t permanently fry your retinas, and it definitely won’t cause skin damage like the UV blast of a tanning bed, so you don’t need to slather on sunscreen just to binge-watch Love Island on your phone. Staring at a screen too long is hard on your eyes not because of blue light, but because of digital eye strain worsened by dry eyes from blinking less. Whether blue light glasses are actually effective is debatable.Blue light does have one real drawback, though, according to University of Georgia optometrist and psychology doctoral candidate Yaw Buabeng. It hampers the eye’s ability to distinguish between light sources. Buabeng and cognitive neuroscientist Billy Hammond, a professor in the University of Georgia’s Behavior and Brain Sciences program, ran a test where they had sixty young adults view different light sources ranging from blue to broadband. After viewing blue light, most of the test subjects had a harder time distinguishing the two separate points of light. It turns out that blue light scatters across the retina more than any other color. People with lighter eyes were less likely to distinguish the sources of blue light, while darker eyes had a slight advantage against light scattering, helping them to perceive the separation between light sources more easily.“Although the influence of wavelength on spectral sensitivity has been extensively characterized, far less is known about how wavelength impacts spatial discrimination thresholds,” Buabeng and Hammond said in a study recently published in Attention, Perception, and Psychophysics. “Understanding how resolution varies across the visible spectrum provides insight into the perceptual consequences of wavelength-dependent optics and the interaction between optical and neural constraints.”While our eyes deal with light scattering even from long wavelengths, the shorter wavelengths of blue light (slightly longer than ultraviolet) can blur vision by preventing light from coming into focus on the retina—imagine trying to focus a smartphone camera when the onscreen image keeps blurring.Action spectra show the biological effects of different types of light, such as absorption or deflection. They’re often used to determine what effects certain wavelengths have on vision, such as the nearly automatic squinting response to glare caused by a burst of short-wave light. But there’s still some uncertainty surrounding exactly how light scatters in the eye. While some studies have suggested wavelength hardly has any effect, others have shown that short waves are more prone to scattering. Even less is known about spatial discrimination.To measure visual performance, the researchers seated each subject in a darkened room, chin and forehead resting on a mount much like the one used in an eye exam, facing a shield with two pinholes of light about five feet away. A patch was placed over the non-dominant eye so that the subject was viewing with one eye only. Each trial began with the two pinholes pushed together so they looked like a single point. The researchers eased them apart until the subject said “two,” then measured the gap with a digital micrometer—the smaller the gap, the sharper the vision at that wavelength. The pinholes were then pushed back together and reset with a different wavelength for the next round. Hammond and Buabeng were testing two hypotheses: that perception of the two points varies by wavelength, and that iris pigmentation affects light scattering in the retina.The results showed that separation between the points of light was easier to see when subjects were looking at broadband light, as opposed to individual wavelengths. Perception of longer waves also differed from shorter waves. Buabeng and Hammond also saw a significant difference in light scattering with differing iris pigmentation. The lighter someone’s eyes were, the more scattering would occur, which means the two points had to be further apart to be perceived as separate. Darker eyes have higher levels of melanin in the iris and in the retinal pigment epithelium, which is in the back of the eye. Melanin absorbs excess light as it scatters, so people with darker eyes need less space between two points of blue light to see them as separate. However, even dark-eyed subjects still needed the blue light points to be further apart than other colors of light they were shown.“Spatial resolution thresholds show systematic wavelength dependence,” the researchers said. “These results underscore the importance of considering wavelength as a determinant of visual performance and suggest that ocular pigmentation may play a protective role in mitigating scatter-related losses.”Elizabeth Rayne is a creature who writes. Her work has appeared in Popular Mechanics, Ars Technica, SYFY WIRE, Space.com, Live Science, Den of Geek, Forbidden Futures and Collective Tales. She lurks right outside New York City with her parrot, Lestat. When not writing, she can be found drawing, playing the piano or shapeshifting.