"Light works as if it’s a drug, except it’s not a drug at all."
-George C. Brainard, PhD, director of the Light Research Program at Thomas Jefferson University in The New York Times (2011).
LED Lighting, Screens and Health
More Screen Sensitivity Literature
Digital Eye Strain (Computer Vision Syndrome) in the scientific literature
"Digital eye strain" (also called Computer Vision Syndrome), is a collection of symtoms surveyed by optometrists and opthalmologists to assess whether screens are impacting the eye health of patients. A commonly-used version of the survey (CVS-Q) asks people hos frequently and how intensely they experience itching eyes, foreign body in the eyes, tearing eyes, excessive blinking, eye redness, eye pain, heavy eyelids, eye dryness, blurred vision, double vision, difficulty focusing for near vision, increased sensitivity to light, colored halos around objects, feeling that sight is worsening, and headache (Segui, M et al., 2015). In addition to the eye symptoms, it's helpful to beginning to understand the broader health impacts of screen flicker that the survey also assesses rates of headache and sensitivity to light.
There have been many surveys of digital eye strain in many countries since the onset of the COVID-19 pandemic, as many groups became interested in the potential harm of increased screen use for work and education. Meta-analysis reviews of this body of scientific literature find that although the prevalence of digital eye strain in individual surveys varies from about 11% to 99%, the overall prevalence when considering all fairly-conducted surveys is 66% to 74% (Anbesu & Lema 2023. Ccami-Bernal et al. 2024, León-Figueroa et al. 2024). Individual surveys typically find that headache is one of the most commonly-reported symptoms and that increased light sensitivity is also common. For example, an Oct. 2021-Jan 2022 survey in the UK (Moore et al, 2024) found that 62.6% of adult survey participants experience digital eye strain, with the most common symptom being eye dryness (66.3%), followed by headache (62.3%). Over 40% of people reported increased sensitivity to light. They found 8.1% of people had symptoms severe enough for them to report that their work was being affected. Surveys like this could underestimate the actual impact of screen use, not only because the symptoms surveyed are limited, but also because people may not notice subtle impacts on their ability to work effectively. This particular survey also excluded people who use screens for less than an hour a day, which would exclude people like me who are severely-enough affected that we need to severely restrict screen use. In general, surveys found that using screens for less time and taking breaks from screens were linked to lower digital eye strain. Surveys largely did not assess what aspects of screens might be particularly injurious, However, one survey of medical radiology residents found that visible flicker on the screen was linked to greater digital eye strain (Junaid Tahir et al., 2024). Together, these surveys indicate that a very large proportion of the population, if not everyone, might be susceptible to physical harm from screen use.Since the people least likely to experience symptoms used screens the least, it's possible that htey, too, could start to experience symptoms with more screen use.
Multiple groups have also surveyed digital eye strain symptoms in children, either by surveying children and teens themselves, or by surveying parents about their children.Chu et al. (2023) surveyed children in 2017-2018 and found that symptoms of digital eye strain increased with more screen use. For example rates of eye fatigue (58.8%), headache (40.1%), and light sensitivity (24.6%) were higher in children using screens more than 4 hours a day than in children using screens less than 1 hour a day (47%, 24.4%, and 12.2%, respectively). Mohan et al. (2020) found that 50% of children experienced digital eye strain during online learning at the beginning of the COVID-19 pandemic (spring 2020), with 54% reporting headache and 35% reporting increased sensitivity to light. Mohan et al. (2020) and Chattinnakorn et al. (2023) in a Dec. 2021-Ja. 2022 survey both found that teens experienced more digital eye strain than younger children, which they attribute to longer screen use by teens.Demirayak et al. (2022) found that headache was the most common symptom (52.2%) for children in May 2021, with use of screens in a dark environment being associated with increased headache.While none of these survey assessed what aspect of screen use is injurious, they strongly implicate screens in harming the physical health of children and are consistent with the possibility that screen flicker could be a factor. The increased symptoms with screen use in a dark environment is one hint that flicker might be an important factor, since flicker can be partially mitigated by sunlight.
There is evidence that student test scores have been falling since 2012 and poor performance is correlated with screen time (evidence in the PISA report and elsewhere discussed by PISA director Schleicher and reviewed by Thompson in The Atlantic). As an educator, I have witnessed the danger of screens being distracting and leading to adverse social interactions and social anxiety that is described in this article. However, I also think LED and screen flicker could very likely be interfering with student learning through (1) impaired ability to concentrate when in light/screens flicker (through impairment of vision/tracking), (2) physiological impairment of health/brain function caused by flicker, and (3) anxiety/depression triggered through physiological changes in the brain triggered by flicker.
Anbesu EW, Lema AK. Prevalence of computer vision syndrome: a systematic review and meta-analysis. Sci Rep. 2023 Jan 31;13(1):1801. doi: 10.1038/s41598-023-28750-6. PMID: 36720986; PMCID: PMC9888747.
Ccami-Bernal F, Soriano-Moreno DR, Romero-Robles MA, Barriga-Chambi F, Tuco KG, Castro-Diaz SD, Nuñez-Lupaca JN, Pacheco-Mendoza J, Galvez-Olortegui T, Benites-Zapata VA. Prevalence of computer vision syndrome: A systematic review and meta-analysis. J Optom. 2024 Jan-Mar;17(1):100482. doi: 10.1016/j.optom.2023.100482. Epub 2023 Oct 30. PMID: 37866176; PMCID: PMC10785422.
Chattinnakorn S, Chaicharoenpong K, Pongpirul K. Cross-Sectional Analyses of Factors Related to Digital Eye Strain Symptoms Among Children Using Online Learning Devices During the COVID-19 Pandemic in Thailand. Clin Ophthalmol. 2023;17:1769-1776 https://doi.org/10.2147/OPTH.S416877
Chu, G.C.H., Chan, L.Y.L., Do, Cw. et al. Association between time spent on smartphones and digital eye strain: A 1-year prospective observational study among Hong Kong children and adolescents. Environ Sci Pollut Res 30, 58428–58435 (2023). https://doi.org/10.1007/s11356-023-26258-0
Demirayak, Bengi; Yılmaz Tugan, Büşra1; Toprak, Muge2; Çinik, Ruken3. Digital eye strain and its associated factors in children during the COVID-19 pandemic. Indian Journal of Ophthalmology 70(3):p 988-992, March 2022. | DOI: 10.4103/ijo.IJO_1920_21
Junaid Tahir M, Aymen U, Mehmood Q, Sohaib Asghar M, Kumari U, Hassan Z, Naz N, Rafiq N, Tayyeb M, Ullah I, Abbasher Hussien Mohamed Ahmed K, Alwalid O. Digital eye strain and its associated factors among radiology physicians in Pakistan: a cross-sectional survey using logistic regression analysis. Ann Med Surg (Lond). 2024 Mar 4;86(4):1933-1941. doi: 10.1097/MS9.0000000000001882. PMID: 38576948; PMCID: PMC10990352
León-Figueroa DA, Barboza JJ, Siddiq A, Sah R, Valladares-Garrido MJ, Adhikari S, Aguirre-Milachay E, Sah S, Rodriguez-Morales AJ. Prevalence of computer vision syndrome during the COVID-19 pandemic: a systematic review and meta-analysis. BMC Public Health. 2024 Feb 29;24(1):640. doi: 10.1186/s12889-024-17636-5. PMID: 38424562; PMCID: PMC10902934.
Mohan, Amit; Sen, Pradhnya; Shah, Chintan; Jain, Elesh; Jain, Swapnil. Prevalence and risk factor assessment of digital eye strain among children using online e-learning during the COVID-19 pandemic: Digital eye strain among kids (DESK study-1). Indian Journal of Ophthalmology 69(1):p 140-144, January 2021. | DOI: 10.4103/ijo.IJO_2535_20
Moore PA, Wolffsohn JS, Sheppard AL. Digital eye strain and its impact on working adults in the UK and Ireland. Cont Lens Anterior Eye. 2024 May 11:102176. doi: 10.1016/j.clae.2024.102176. Epub ahead of print. PMID: 38735811
Schleicher, Andreas. PISA 2022: Insights and Interpretations. OECD Programme for International Student Assessment. https://www.oecd.org/pisa/PISA%202022%20Insights%20and%20Interpretations.pdf
Seguí Mdel M, Cabrero-García J, Crespo A, Verdú J, Ronda E. A reliable and valid questionnaire was developed to measure computer vision syndrome at the workplace. J Clin Epidemiol. 2015 Jun;68(6):662-73. doi: 10.1016/j.jclinepi.2015.01.015. Epub 2015 Jan 28. PMID: 25744132.
Thompson, Derek. It Sure Looks Like Phones Are Making Students Dumber: Test scores have been falling for years—even before the pandemic.The Atlantic, December 19, 2023. https://www.theatlantic.com/ideas/archive/2023/12/cell-phones-student-test-scores-dropping/676889/
Cybersickness in the scientific literature
Cybersickness, reviewed in Stanney et al., 2020, is described as a condition mimicking classic motion sickness that is associated with using virtual reality (VR) or augmented reality (AR) technologies. Symptoms include "nausea, disorientation, oculomotor disturbances, drowsiness (a.k.a sopite syndrome) and other discomforts" (Stanney et al., 2020). Symptoms that may linger long after the VR or AR experience "can compromise postural stability, hand-eye coordination, visual functioning, and general well-being" (Stanney et al., 2020). Most of the population is susceptible to cybersickness (Stanney et al., 2020), although motion sickness susceptibility can vary over a 10,000-fold range in different people (reviewed in Lackner, 2014). The cause of cybersickness is unknown, with over ten proposed hypotheses (Stanney et al., 2020), including the hypothesis that cybersickness results from sensory discordance - disagreement in how the eyes, ears, and body perceive motion (discordance of visual, vestibular, and proprioceptive sensing of motion, respectively). Most research has focused on determining strategies for avoiding inducing cybersickness in VR and AR, although modern systems still induce cybersickness and research demonstrating that current technology is an improvement on previous generations is lacking (Stanney et al., 2020). NASA and the US military have interests in work on VR and AR, including the mitigation of cybersickness (Stanney et al., 2020). In a similar scenario, the use of night vision goggles when flying has been reported to cause migraine headache, spatial disorientation, and balance issues in a military helicopter pilot (Cho et al., 1995). While viewing the night vision display screen itself could be problematic, it's also possible that the rotating helicopter blades could be an enhanced source of flicker on the night vision display.
Requirements for VR or AR use for training or performance of one's job could prevent individuals susceptible to cybersickness from undertaking some careers.
"We would argue that the magnitude of this cybersickness problem, and its implications to job performance and career progression, are poorly understood by society in general. This is not only due to problems with existing hardware, which are likely to be resolved, but with a lack of understanding of how cybersickness manifests, varies across individuals, and how it may be mitigated. This lack of understanding has resulted in a deemphasizing of the importance of cybersickness research being conducted, and rather a push for cybersickness as being something users will eventually just adapt to" (Stanney et al., 2020).
Stanney et al., 2020 provide an updated proposal for research and development priorities that are urgently needed and critically important to eliminate cybersickness.
Also see notes in Anecdotal reports of LED sensitivity and in Background: LED Screens on the use of flicker as a strategy to reduce screen blur effects that may contribute to cybersickness.
"Cybersickness" has also been suggested in anecdotal reports (see Anecdotal reports of LED sensitivity) as the explanation for adverse health effects experienced by users of normal screens like cell phones and tablets.
Cho AA, Clark JB, Rupert AH. Visually triggered migraine headaches affect spatial orientation and balance in a helicopter pilot. Aviat Space Environ Med. 1995 Apr;66(4):353-8.
Lackner, J. R. Motion sickness: More than nausea and vomiting. Experimental Brain Research, 232 (2014) 2493–2510. https://dx.doi.org/10.1007%2Fs00221-014-4008-8
Stanney, K. et al. Identifying causes of and solutions for cybersickness in immersive technology: Reformulation of a research and development agenda. International Journal of Human-Computer Interaction, 36 (2020) 1783-1803. https://doi.org/10.1080/10447318.2020.1828535
Could screen flicker contribute to Zoom fatigue?
As increased videoconferencing during the COVID-19 pandemic led to widespread reports of "Zoom fatigue," scientists hypothesized that various psychological stress factors could lead to both physical and mental fatigue (Bailenson, 2020). A Zoom Exhaustion & Fatigue Scale questionnaire (Fauville et al., Feb. 2020) assessed general physical or mental fatigue, vision blurriness, eye pain or irritation, and mental fatigue or irritability in social, motivational, and emotional areas. This questionnaire was distributed to thousands of individuals along with an open-ended question, questions addressing the psychological experience during a videoconference, and a question set assessing personality. There was a correlation among the general, visual/eye, emotional, motivational, and social fatigue scores that correlated with the amount of time spent in videoconferences, with women scoring higher than men (Fauville et al., April 2020). Several psychological factors helped to explain why videoconferences can be stressful.
While the Zoom study focuses on psychological factors contributing to Zoom fatigue, it does not assess or rule out the possibility that there could also be a physiological cause of symptoms, at least for a subset of individuals or as a contributing factor more broadly. It is interesting that many of the symptoms assessed in the Zoom study are also among the symptoms reported by individuals who are more generally sensitive to LED lights and/or screens, such as physical fatigue, vision blurriness, eye pain/irritation, irritability, and descriptions of mental fatigue that suggest feeling anxiety. The "mental fatigue" that is reported in Zoom fatigue could overlap with the concentration and short-term memory problems reported by individuals who are sensitive to LED lights and/or screens. Since the Zoom video feed can be a source of visible screen flicker (see Background: LED Screens), and given the known health effects of visible flicker (see Flicker below 100 Hz) it would be interesting to assess to what degree that flicker, as well as the flicker associated with any increase in screen use overall, contributes to Zoom fatigue symptoms. It would also be interesting to assess other physiological symptoms such as headache.
Bailenson, J. Why Zoom Meetings Can Exhaust Us. Wall Street Journal, April 3, 2020. https://www.wsj.com/articles/why-zoom-meetings-can-exhaust-us-11585953336
Fauville, et al. Nonverbal Mechanism Predict Zoom Fatigue and Explain Why Women Experience Higher Levels Than Men. SSRN Electronic Journal. April 14, 2021. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3820035#
Fauville, et al. Zoom Exhaustion & Fatigue Scale. SSRN Electronic Journal. February 23, 2021. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3786329