Have you ever seen a picture of New York City, or any other big city, at night? Have you noticed the brightened skies surrounding it? If so, you’ve observed skyglow, a form of light pollution. It is so prevalent that in a 2016 study, researchers found that internationally, about 83% of the population lives under it. [1]
The International Dark-Sky Association defines light pollution as the use of artificial light in an excessive or inappropriate manner arising from different sources, such as building exterior and interior lighting, streetlights, and illuminated sports venues [2], [6]. It is known that light pollution can impact our environment through increased energy consumption and disruption of ecosystems and wildlife. It can also prevent us from observing nature, with about one-third of the world’s population and 80% of people in North America not being able to see the Milky Way. What’s more, it can affect our health via disruption of our circadian rhythm and, thus, sleep. [2], [7], [8] But what about the organ that takes in the stimulus? Does light pollution directly affect our eyes? If so, how?
To answer these questions, we need to first understand how light interacts with our retinas. Visible light has a wavelength range of 380-780 nm, and the amount of visible light we can perceive, or light intensity, is measured through illuminance. Thus, the higher the illuminance, the greater the light intensity, and the brighter the light. [4], [5] Our retina, the most light-sensitive layer of the eye, is constantly at work perceiving changes in brightness.
The inner workings of the retina are complex but can be thought of as having many parallel circuits working simultaneously; certain circuits adapt to specific light conditions [9]. Much like flipping a switch on, light often acts as the initiator of a cascade of connections. Its projection on the retina has two important roles which are mediated by a slew cells, including the rod and cone photoreceptor cells, the retinal ganglion cells (RGCs), and retinal pigment epithelium cells (RPEs). The retina’s first role is to control for adequate visual function, like seeing color, and the second involves non-imaging tasks like maintaining our 24-hour biological clock via circadian rhythms. As a result, the retina must maintain the balance between sensitivity and saturation due to changes in light intensity throughout the day. Yet, while the retina has several protective mechanisms against certain kinds of light exposure, current modern life habits may cause damage. [3], [9], [10]
Figure 2. A magnified representation of the retinal structure with different circuit-like connectivity among the various
cell types.
Excessive artificial light can promote retinal damage or accelerate existing retinal disease through distinct mechanisms. One such type is photothermal, which causes a rise in tissue temperature and can promote protein breakdown in the retina. Another type is photochemical, where a series of chemical reactions are activated. One such example is oxidative stress, where certain molecular interactions result in the breakdown of membrane structures and potential death of photoreceptor cells and RPEs, given both cell types are highly oxygenated and sensitive to oxygen imbalance. Yet, the severity of the damage depends on different factors, such as light wavelength. For instance, some work has shown that wavelengths in the 320-440 nm range resulted in different types of retinal damage compared to the 470–550 nm range. Overall, shorter wavelengths increase damage, specifically near the ultraviolet spectrum, which, according to one study, caused irreparable injury to rod and cone photoreceptor cells. [3]
Another important parameter is light intensity; both artificial bright and low visible light can severely impact the retina. One rodent study using bright light resulted in photoreceptor cells’ death by apoptosis. For low light studies, some researchers have found it can cause ultrastructural cellular changes, which can also lead to cell death. What’s more, just like how continuous or intermittent exposure to the sun, no matter how bright the day, can impact our skin, another factor that greatly influences the effect of artificial low light is the period of light exposure. A series of animal studies have each found that constant or continual exposure to low light can result in greater activation of retinal degeneration-related enzymes, irreversible photoreceptor cell death, and cause structural changes in the RPE. [3]
Aside from direct retinal damage, low light intensities can also cause indirect damage, as found by a recent study that assessed the impact of dim light on humans during sleep. Results found that exposure to dim light disturbed normal sleep by disrupting the circadian rhythm, possibly due to oversaturation of the RGCs. Exposure also increased eye fatigue the following morning, possibly causing eye discomfort and symptoms such as tired, blurry, and/or burning eyes. [3], [11]
In all, though the effects of light pollution on our vision are concerning and are still being studied, there are practical steps we can take to significantly and immediately reduce the risks to our health and habitat. Starting in our homes, we should use lighting when and where it’s needed, install motion detector lights and timers for outdoor lighting, and use filters to block out potential unsafe wavelengths, such as the blue light emitted from the increasingly common light-emitting diodes (LEDs), and choose warmer lighting colors (longer wavelengths). [2], [3], [13] Though further studies are needed, we know that we can work together to reverse the effects of light pollution and, thus, protect ourselves and our surroundings.
References:
[1] F. Falchi et al., “The new world atlas of artificial night sky brightness,” Science Advances, vol. 2, no. 6, p. e1600377, Jun. 2016, doi: 10.1126/sciadv.1600377.
[2] “What is light pollution?,” DarkSky International. https://darksky.org/resources/what-is-light-pollution/ (accessed Jul. 30, 2023).
[3] M. A. Contín, M. M. Benedetto, M. L. Quinteros-Quintana, and M. E. Guido, “Light pollution: the possible consequences of excessive illumination on retina,” Eye (Lond), vol. 30, no. 2, pp. 255–263, Feb. 2016, doi: 10.1038/eye.2015.221.
[4] “Read Our Ultimate Guide To Lux vs Lumens vs Watts For Lighting Installations | Warehouse & Factory Lighting,” Green Business Light. https://greenbusinesslight.com/resources/lighting-lux-lumens-watts/ (accessed Jun. 19, 2023).
[5] “FARLabs.” https://www.farlabs.edu.au/structure/explain-photoelectric-effect/ (accessed Jun. 19, 2023).
[6] S. D. published, “Light pollution: Environmental impact, health risks and facts,” livescience.com, Apr. 05, 2022. https://www.livescience.com/light-pollution (accessed Jun. 18, 2023).
[7] E. S. Briolat, K. J. Gaston, J. Bennie, E. J. Rosenfeld, and J. Troscianko, “Artificial nighttime lighting impacts visual ecology links between flowers, pollinators and predators,” Nat Commun, vol. 12, no. 1, Art. no. 1, Jul. 2021, doi: 10.1038/s41467-021-24394-0.
[8] “Light pollution has complex effects on animal vision,” ScienceDaily. https://www.sciencedaily.com/releases/2021/07/210706102041.htm (accessed Jun. 18, 2023).
[9] “Eyes have a natural version of night vision: Cells in retina change their duties to help the brain detect motion,” ScienceDaily. https://www.sciencedaily.com/releases/2018/09/180913113930.htm (accessed Jun. 18, 2023).
[10] “Gap Junctions Contribute to Differential Light Adaptation across Direction-Selective Retinal Ganglion Cells – ScienceDirect.” https://www.sciencedirect.com/science/article/pii/S0896627318307244?via%3Dihub (accessed Jun. 19, 2023).
[11] Y.-W. Suh, K.-H. Na, S.-E. Ahn, and J. Oh, “Effect of Ambient Light Exposure on Ocular Fatigue during Sleep,” Journal of Korean Medical Science, vol. 33, no. 38, Aug. 2018, doi: 10.3346/jkms.2018.33.e248.
[12] info@noirlab.edu, “Infographic Illustrating the Impact of Light Pollution on Our Ability to See Stars and Other Objects in the Night Sky,” www.noirlab.edu. https://www.noirlab.edu/public/images/noirlab2302a/ (accessed Jul. 30, 2023).
[13] Staff, “Assess your home’s outdoor lighting,” DarkSky International, May 13, 2023. https://darksky.org/get-involved/home-lighting-assessment/ (accessed Jul. 30, 2023).
Author:
Nina Sara Fraticelli-Guzman is a current Bioengineering PhD student at the Georgia Institute of Technology. Her research focuses on studying women’s vision health, specifically researching how menopause can impact ocular tissue mechanics and how that can be correlated to diseases such as glaucoma. Outside of the lab, Nina Sara enjoys sports and reading.
Editors:
Ananya Sen is currently a science writer at the Carl R. Woese Institute for Genomic Biology. She completed her Ph.D. in Microbiology at the University of Illinois at Urbana-Champaign in 2021. She is an ardent reader and will happily discuss anything from Jane Austen to Gillian Flynn. Her travel goals include covering all the national parks in the U.S. with her sidekick Oscar, a Schnauzer/Pomeranian mix.
Roopsha Sengupta is the Editor-in-Chief at ClubSciWri. She did her Ph.D. at the Institute of Molecular Pathology, Vienna, and postdoctoral research at the Gurdon Institute, University of Cambridge, UK, specializing in the field of Epigenetics. During her research, she was involved in many exciting discoveries and had the privilege of working and collaborating with a number of inspiring scientists. As an editor for ClubSciWri, she loves working on a wide range of topics and presenting articles coherently while nudging authors to give their best.
Image credits-
Cover image: iStock
Figure 2- created with Biorender
This article was initially submitted to the ComSciCon Flagship 2023 Create-a-thon workshop and further improved by the editorial process at Club SciWri. Club SciWri and ComSciCon have a shared mission of helping scientists make science accessible for all.
