Anecdotal reports including expert opinion:
ARC: Lighting in Architecture: Human Centric Lighting - The New X Factor?, December 12, 2018
Describes the rationale of convening a panel of experts in the UK on "human-centric lighting" and proposes an alternate terminology for ideal lighting: "Research Informed Human Light (RIHL)." Suggests that members of the public are being used as unwitting guinea pigs in lighting designers' uncontrolled, unlicensed medical experiments. This is because light affects human health in a manner similar to drugs, but new lighting designs are being distributed to the public without the same kind of scientific studies and safeguards that accompany drug development. The short and long-term health effects of LED lighting are unknown. This article describes the serious gaps in the medical literature. While the article briefly mentions flicker, it mostly discusses the potential effect of color temperature on circadian rhythms.
School Construction News: The Health and Cost Benefits of Flicker-Free Lighting, by John Davenport, Energy Focus, Inc., December 5, 2019
Describes how installing flicker-free LED lighting in a particular Ohio elementary school had benefits in terms of health and cost compared to the prior fluorescent lighting. In terms of health, the article focuses on how fluorescent lights flicker and how flicker-free LEDs eliminate that feature of the lighting, implying that by "flicker-free," the author is referring to completely flicker-free LEDs that lack all flicker (temporal modulation), rather than only referring to lights that only lack obviously visible flicker. The article does not compare the effects of commonly-available flickering LED lights to other types of lighting, although the implication of the article would be that installing LED lights with worse flicker than fluorescent lights might be detrimental to human health and the learning environment. The article also references that the health and cost-saving benefits of flicker-free LED lighting have been recognized by 230 leading educational institutions that have installed flicker-free LEDs.
IEEE Spectrum: The iPhone 12 mini makes me sick (literally), by Tekla S. Perry, Senior Editor, June 11, 2021
Includes an interview with physicist and display expert, Raymond Soneira, CEO of DisplayMate Technologies, who reports "hundreds of inquiries over the years regarding this issue, with people complaining of display flicker causing a wide range of symptoms, from visual fatigue, to headaches and nausea, up through seizures and photo-triggered epilepsy—which is the extreme version of flicker sensitivity. In many cases the flicker is subliminal. Some people just feel unusually tired or uncomfortable and don't know why." Notes that there have been sufficient reports of sensitivity to Soneira from individuals both within the display industry and well-known journalists/TV anchors that he believes it's a "real effect."
UK charity trying to raise awareness of health problems associated with LED lights, including "eye pain, headaches and migraines, skin rashes, burning, dizziness and nausea." They further report medical issues reported to their site by individuals that include exacerbation of medical conditions like migraine as well as many reports of new symptoms in previously healthy individuals that include both severe symptoms like "searing eye pain, debilitating headaches, skin burning and rashes, dizziness, fainting and vomiting" as well as milder symptoms like "anxiety, eczema, edginess or just a sensation of discomfort or ‘wrongness’ that is hard to locate." They also suggest that medical professionals are concerned about "human eyes, skin, circadian rhythm and nervous system" in terms of the effects of LED lighting. Importantly, LightAware is advocating for the human rights of individuals sensitive to LED lighting for whom a shift to only LED lighting outside of the home may prevent access to "workplaces, healthcare, education, recreation, public transport or places of worship." I would personally add that access to groceries is also a significant issue. The LightAware site suggests that brightness, color temperature, and flicker from LED lights might all be issues, but their site is limited by the lack of scientific research needed to identify the actual issue(s).
National Geographic: Endless scrolling through social media can literally make you sick, May 17, 2021
Describes how symptoms of "cybersickness," previously associated with virtual and augmented reality, are also experienced by users of normal screens. Includes experts commenting on the similarity between cybersickness and motion sickness and speculation on the reasons for increased reports of cybersickness during the Covid-19 pandemic.
OLED-info: Pulse-width modification (PWM) in OLED displays
Suggests that 10% of people are bothered by PWM of screen backlights, including "headaches and even migraines," while a smaller percentage "suffer very badly and the flickering may result in other health issues." No reference is given for this assertion, other than reports from screen users to the website and to other individuals quoted in the article. Includes advice from Raymond Soneira, CEO of DisplayMate Technologies.
The Irish Times: Campaigner claims Led lighting can cause headaches and nausea: Calls for more research as state invests millions switching to more efficient lights, April 18, 2022
Describes the calls from Elaine Dennehy of County Galway, Ireland, for research on LEDs. LED lights cause her such severe, long-lasting headaches and nausea that she moved in 2014 to a rural location to avoid LED lights, but has since become virtually confined to her home due to the increasing introduction of LED lights. She shares her story here.
Many websites report sensitivity to LED lights or screens, especially headaches, disorientation/nausea, and various kinds of pain in or near the eyes. Terminology to describe screen sensitivity varies widely and includes "digital eyestrain," "computer vision syndrome," "cybersickness," "digital motion sickness," "simulator sickness," and "Zoom fatigue." It is unclear to what extent the causes and symptoms of these phenomena overlap and how often they occur. More anecdotal reports than those described below may be found by searching for these terms. Additionally, multiple eyeglass providers are now marketing blue-blocking lenses that they suggest may provide protection from adverse health effects of LED lights and screens.
BlurBusters.com: Motion Blur Reduction
A strategy for reducing screen motion blur in VR and AR is to strobe the backlight on very briefly each frame after the monitor has finished refreshing the pixels. Alternatively, black frames can be interspersed between the normal image frames, creating a similar effect. Either the use of a strobing backlight or black frame insertion creates flicker. BlurBusters.com mentions that some of their readers are more bothered by motion blur, some are more bothered by the flicker created with motion blur reduction strategies, and some are bothered by both. (See LED Screens).
DXOMARK: Flicker, the display affliction
Hypothesizes that the discomfort people experience from screen flicker results only from eye overuse due to repeated expansion and contraction of the pupil (iris muscles) because of the eye's attempt to respond to the flicker. There is not yet any scientific evidence to support the hypothesis that overuse of eye muscles is the problem for people with flicker sensitivity. Available data contradict the hypothesis that the pupil repeatedly expands and contracts in response to screen flicker. The pupil only expands and contracts when flicker is slower than about 3 Hz, although the pupil tends to be slightly smaller when there is flicker up to about 30 Hz than when there is not flicker (reviewed in Brundrett, 1974). Regardless of the arguments about cause, this website does note flicker sensitivity to be a reported problem.
NBCNews: Is iOS7 making you feel sick? Here's why, September 29, 2013 and ExtremeTech.com: iOS7 nausea and cybersickness - What causes it, and why it's a sign of things to come, September 30, 2013
Describe widespread reports of symptoms similar to motion sickness caused by looking at screens.
OSX Daily: Managing PWM on OLED iPhone & iPad displays
Notes that users of screens with PWM have "eye strain, feel nauseous or dizzy, or have headaches from the screen flickering."
TheConversation.com: Screentime can make you feel sick - here are ways to manage cybersickness
A graduate student researching the phenomenon includes links to references on cybersickness and motion sickness.
WikiHow: How to avoid iPhone or iPad nausea
Suggests that headaches and nausea due to screen use are well-known problems that are wide-spread. Evidence is not provided.
WaveformLighting.com reviews of flicker-free LED light bulbs
Reviews of flicker-free light bulbs (2700K and 3000K or 4000K-6500K) include many users who report choosing the flicker-free LED bulbs because they do not cause various adverse health effects. Out of 72 reviews of the 2700K and 3000K bulbs, 30 mention the flicker-free quality, 8 report purchasing the bulbs to avoid migraines or headaches, 5 report purchasing to avoid eye strain, 5 report the bulbs making them feel calm, 10 report purchasing because the bulb is in some other way beneficial for their health, and 37 reviews do not mention any of the above. Of the 37 reviews not mentioning any of the keywords, 12 of those are clustered as the earliest 12 reviews spanning May 26, 2018 – February 24, 2019, and most of the 25 later reviews refer to the high color rendering index of the bulbs. (Waveform lighting Centric Home 2700K and 3000K A19 reviews, accessed May 9, 2021).
Forums for people sensitive to LED screens and/or lights:
A forum specifically for individuals with screen and/or LED light sensitivity. Many descriptions of individuals' symptoms are provided. Attempts to find lights and screens or screen conditions that do not trigger symptoms are also reported. Contributors to the LEDStrain Forum generally report a subset of eyestrain, migraine, headaches, neck pain, nausea, and difficulty concentrating that they attribute to using LED screens and/or LED lights. Many report pain in the eyes or head when they are actually exposed to the screen/lights. There is a lack of consensus among contributors as to how to label their health problem if it doesn’t fall neatly into the “eyestrain” category and some report headaches with concentration problems but don’t think of them as migraine. A large percentage of contributors work in computer technology or have a high level of tech savvy and are trying to collectively solve which parameters of LED screen hardware and computer software are causing their health problems. The vast majority of contributors only began to experience their health issues since they started using LED screens and/or lights. While a small number of contributors have rare health or eye conditions that they think provide explanations for their symptoms, the consensus hypothesis among most contributors has increasingly coalesced around the hypothesis that various forms of flicker are the cause of their LED screen sensitivity and LED light sensitivity. The vast majority of contributors do not report blue-light blocking glasses being a solution for their problem.
Individual threads on various forums, including MacRumors Forums and the Apple community forum.