Based on these survey data, and until rigorous scientific studies can be conducted to delineate safe parameters for light flicker, I advocate for the following:

For lighting manufacturers and lighting professionals:

  • Manufacturers in the US are required to relay reports of health problems from LED devices to the FDA: How to report health problems with LED lights or LED screens to the FDA.

  • Lighting manufacturers should include the proper circuitry so that they completely eliminate flicker from their LED lights. In the current language used by lighting manufacturers, they should completely eliminate all "temporal light modulation" from their lights, regardless of whether normal control individuals know that they can see it. This will not only protect the sensitive, but may also (hopefully, for the sake of the environment) further speed adoption of LED lights by the public, by eliminating a quality that may make people dislike LEDs. Too few US manufacturers are producing completely flicker-free LED lights now, although many manufacturers, including Philips, did so in the past. To my knowledge, the only current US manufacturer of completely flicker-free household LED bulbs is the small company, Waveform Lighting.

  • Lighting professionals should stop using language and flicker metrics that have the effect of creating confusion and obfuscation about LED light flicker. First, the 2015 IEEE report distinguished between "visible" and "invisible" flicker, with both kinds being implicated in causing adverse health effects, with seizures from visible flicker and headaches and eyestrain from "invisible" flicker (IEEE std 1789, 2015). Then, in 2016 the lighting industry decided that "invisible flicker" would no longer qualify as "flicker" at all and what they previously called "flicker" would now be called "temporal light modulation" and only "visible flicker" would be called "flicker" (CIE TN-006).

I think "flicker" should mean "flicker." Especially because the public needs to understand, "flicker" should be used in the sense that it is used by the general public and in the sense that it was often used by the lighting industry prior to 2016. Otherwise, how can the average person receive comprehensible information from the lighting industry? The lighting industry's current insistence that certain flicker is "temporal light modulation" but isn't "flicker" if it's not obviously visible creates considerable confusion. For example, using their industry-specific jargon, lighting professionals can currently tell people that the lights "don't flicker" even if they do flicker, as long as their flicker (temporal light modulation) isn't visible to average normal observers. This is despite the fact that research has shown that people can have headaches and eye strain due to flicker whether or not they consciously see it (see Background: Health Effects, including Brundrett, 1974, discussed in Background: Health Effects of flicker below 100 Hz).

The ability of lighting professionals to deny the existence of flicker through industry-specific language can increase the likelihood that third parties, like employers or medical professionals, might dismiss the health concerns of sensitive individuals. Sensitive individuals face an uphill battle convincing others that they are hurt by light that doesn't hurt most people. They face medical professionals who might dismiss their condition as psychosomatic (see discussion of the "sunglasses sign" in Background: Unanswered questions), they face employers who might question their truthfulness or mental health, they face lighting consultants who have a monetary interest in not admitting that the lights they have specified are unhealthy, and they face lighting manufacturers that are not likely to appreciate reports that their products are unsafe. Sensitive individuals, who may be experiencing significant neurological symptoms, should not also be burdened with navigating unnecessarily confusing industry-specific language.

Pst and SVM are not useful metrics for protecting sensitive individuals from flicker ≥100 Hz that is produced by LED lights. Pst is only used for flicker <80 Hz. SVM is a measure of flicker visibility based on average normal observers and the current SVM limit proposed by the lighting industry is much more permissive of flicker than the previously-developed IEEE recommendations (see Background: LED lights). My personal experience is that the IEEE recommendations for flicker are not close to stringent enough (see Self-tests). None of these current metrics are based on any studies of the health effects of flicker ≥100 Hz.

  • The lighting industry should stop assuming that the visibility of flicker equates with whether flicker produces health effects. There is no data to support this assumption. Additionally, visibility is quite subjective and dependent on testing conditions. As mentioned above, research has shown that people can have headaches and eye strain due to flicker whether or not they consciously see it (see Background: Health Effects, including Brundrett, 1974, discussed in Background: Health Effects of flicker below 100 Hz).

  • Lighting professionals should stop arguing that it's not important to limit flicker in venues that people might pass through transiently. No one has established a safe exposure time for sensitive individuals. My personal experience is that seconds of exposure to flicker can be enough to trigger serious health effects for me. Also, brief individual exposures to the hundreds of flickering LED lights that I encounter on a short walk in New York City have a cumulative effect. Flickering LEDs have become so ubiquitous in public places that they can't be considered to act transiently in isolation from each other.

For policy makers:

  • Since light flicker can have adverse physiological effects on the human nervous system and can create neuroinflammation (see Background: Health Effects), lights that flicker should undergo the testing and regulation of medical devices.

  • Policy makers should require completely flicker-free circuitry in LED lights and should require that LED lights are actually completely flicker-free upon independent testing.

  • Policy makers should require manufacturers to publicly disclose flicker metrics for their LED lights, including percent flicker, flicker frequency, flicker index, and a graph of light output vs. time. (On such a graph of light output vs. time, it's obvious whether the graph is a flat line, meaning that the light is completely flicker-free, or whether there is repetitive flicker. Other metrics are more difficult to interpret). They should require language from the lighting industry that clearly informs the public about flicker, rather than creating obfuscation through an industry-specific, limited definition of flicker.

  • Access to environments with safe lighting should be viewed as both a basic accessibility issue and a basic public health issue. Since no one yet knows what level of light flicker is safe for sensitive individuals, in the interim, completely flicker-free LED light should be required in any setting subject to public health law.

  • LED flicker should be eliminated from the environments of particularly vulnerable individuals, such as the homes of children, schools, hospitals, and institutional residential settings.

  • LED flicker should be eliminated from all venues accessed by the general public, but especially those needed for meeting basic needs, such as groceries, pharmacies, medical offices, public transportation, and urban sidewalks. Flicker should be eliminated in vehicle lights and in street illumination. Lights inside public transportation vehicles should not flicker. LED signs that flicker should be remodeled to eliminate the flicker or should be removed from public places. For example, LED signs on New York City sidewalks, at bus stops, on subway platforms, and, recently, on some subway trains have significant flicker that makes it impossible for sensitive individuals to walk on the sidewalk or take public transportation without encountering triggering flicker.

  • In locales like New York City where incentives for light replacement or policies for increased energy efficiency led to the recent widespread installation of LED lights with flicker (because those were virtually the only kind of LEDs in the marketplace recently and there is a lack of awareness of the issue), programs should be created to help businesses and individuals to replace the unhealthy flickering LEDs with completely flicker-free LED alternatives, both in terms of helping to identify flicker-free technology and to provide financial support for the correction, especially to individuals and small businesses.

For scientists and engineers:

  • Scientists should begin to do both clinical and basic research on the health effects of ≥100 Hz flicker, such as the flicker of LED lights and the numerous complex forms of flicker that may be viewed on LED screens.

  • Scientists should determine how to test people for flicker sensitivity. It is particularly important to be able to screen children for flicker sensitivity before exposure to flicker at home or school impacts their learning.

  • Lighting engineers should shift their focus from developing various forms of flickering LED lights to further improve upon existing completely flicker-free LED technology.

  • Engineers should develop an intuitive, reliable, and low-cost flicker meter that will allow sensitive individuals to detect flicker in new environments without needing to observe more flicker. For example, my current strategy of using a slow-motion smart phone video (see Self Tests) isn't effective for the most subtle flicker and has the significant problem of exposing me to more flicker when viewing the video playback. Among other flicker metrics, a flicker meter should include a graph of light output vs. time so that the waveform shape can be readily viewed. The flicker meter should also readily report about multiple kinds of flicker for lights that have more than one type, such as when LED lights controlled by a driver have faster than 120 Hz flicker, but also have a residual 120 Hz component to the flicker because of insufficient elimination of flicker from the AC mains. The screen on the device should be free of flicker. An eInk screen that only refreshes when a new reading is requested would be ideal.

For medical professionals:

  • Medical professionals should develop tools for distinguishing between different kinds of photophobia in patients, including between sensitivity to light brightness, sensitivity to light flicker, or sensitivity to particular wavelengths of light. Sensitivity to constant light sources, like sunlight or completely flicker-free LEDs, should be compared to sensitivity to LEDs with flicker. Those who report sensitivity to LEDs tend to not be bothered by a moderate level of sunlight and may even find that sunlight is in some way helpful. Since LED-sensitive individuals tend to become even more sensitive when experiencing symptoms, and perhaps generally over time, other forms of flickering light that might not have been bothersome in the past might become bothersome, including fluorescent lights and even halogen or traditional incandescent lights.

  • Medical professionals should begin to consider flicker sensitivity as a relatively new medical condition with flicker as a novel trigger and with a collection of symptoms that may require evaluation distinct from that for previously-characterized disorders. It should be recognized that while many sensitive individuals do know that LED lights and/or screens are their triggers, especially if they have an immediate adverse reaction, others may not have yet realized that LEDs cause their symptoms, especially if their symptoms take time to build following exposure, or if their symptoms are currently subtle. Additionally, even if individuals know they are sensitive to LED lights and/or screens, they may not have the tools to figure out whether flicker or some other aspect of the light is the problem.

  • Medical professionals should recognize that light flicker may initiate neuropathology in some people, and these individuals may experience both acute symptoms during and immediately after the flicker "injury" as well as persistent symptoms that may last weeks or months. Repeated exposure to flicker may repeatedly re-initiate the disease process and may lead to an increase in symptom severity over time. It may be more appropriate to treat flicker exposure as a novel form of mild brain injury (likely with both central and peripheral nervous system involvement) for sensitive people than it is to try to explain their symptoms as only sequelae of other preexisting conditions, although these conditions, like migraine, dry eye, concussion, or other conditions with photophobia, may certainly increase the likelihood of flicker sensitivity or have disease processes that interact with the flicker-induced disease process.

  • Medical professionals should report patients experiencing health effects from LEDs to appropriate government agencies. Health issues with LED lights or screens should be reported to the US Food and Drug Administration, which welcomes these reports from both inside and outside the US. How to report health problems with LED lights or LED screens to the FDA.

For health departments and health-related government agencies:

  • Health departments and government agencies should recognize sensitivity to flickering lights as a public health issue, given the wide-scale anecdotal reporting of adverse effects and particularly considering the severity of the neurological symptoms reported in this Survey.

  • Health departments should provide a mechanism for people to report harmful light flicker in public places, in the US should help to relay reports from individuals to the FDA, and should help sensitive individuals find essential businesses and services that are accessible because they are free of light flicker.

  • Government agencies like the US Food and Drug Administration that regulate products that emit radiation, including visible light, should provide a clear mechanism for doctors and patients to report adverse health effects of such products. As of August 2022, the US Food and Drug Administration has communicated that health issues with LED lights or screens should be reported to the them as described here - they welcome reports from both inside and outside the US: How to report health problems with LED lights or LED screens to the FDA. Our reporting through this avenue will be essential to inform future regulation, legislation, and to justify funding research.

For businesses and the building design industry:

  • Businesses should consider providing lighting that doesn't cause harmful neurological health effects to be a basic public health issue as well as an accessibility issue, regardless of whether the law has yet caught up to requiring this.

  • Businesses should require completely flicker-free lighting be used in new construction and renovations. Businesses should know that there is not yet any known safe level of flicker and current flicker metrics and recommendations do not result in safe levels of flicker. Lighting designers and architects should review data about the flicker of light fixtures and bulbs before choosing them for projects. Business owners should have an independent lighting consultant that is different from the manufacturer or consultant who chose the lights for the project evaluate the flicker of the lights in situ. They should evaluate whether the specified lighting equipment was actually used in the project and whether the lights flicker following installation. Lighting control systems or dimmer systems common to business installations might themselves introduce flicker. The entire lighting system needs to be tested for flicker in the actual building following completion of installation. Especially if sensitive individuals indicate that the lights may be unhealthy, only considering manufacturers' descriptions of lighting is insufficient. The actual lights that are harming people should be tested. They should be tested without sunlight or other lights on in the room. Full room readings of flicker are insufficient to identify which lights flicker. A low level of flicker does not indicate that the lights aren't affecting the health of sensitive individuals - the safe level is unknown.

  • Use daylight to light buildings when possible - it has energy-saving, psychological, and physiological health benefits.

Edwards, L. & Torcellini, P. A Literature Review of the Effects of Natural Light on Building Occupants, National Renewable Energy Laboratory TP-550-30769, July 2002.

For the computer, television and video industries

  • Manufacturers in the US are required to relay reports of health problems from LED devices to the FDA: How to report health problems with LED lights or LED screens to the FDA.

  • Screen hardware designers should eliminate flicker from screen backlights or other screen hardware that can produce flicker.

  • Software designers should stop using flicker of luminance or color as a strategy in image-rendering. Software designers should stop using flicker to create cosmetic visual effects. Software designers should also stop using moving repetitive images for cosmetic effects, such as having repeating waves of subtle colors move across a screen to indicate content is loading, as repetitive patterns can also be noxious to sensitive individuals, and when patterns move on a screen, they appear to flicker. As an accessibility feature, there should be an alternative to scrolling that animates the scrolling process - for example, this can be done some of the time by clicking on the portion of the scroll bar below the scroll handle to jump to the next part without animation, but in some software, this just rapidly animates the scroll, creating flicker.

  • Video producers should avoid introducing flicker, including all of the forms of video flicker described in Background: LED Screens.

For parents and educators:

  • Ensure that lights in your home and your child's school are free of light flicker. Since indications are that flickering LED light may impact concentration and short-term memory in sensitive individuals and that sensitive individuals become more sensitive to flicker with more exposure (see Survey: Discussion and Self-tests), LED flicker might impact the learning of sensitive children. There is not yet a way to identify sensitive children.

  • The only artificial lights without flicker are completely flicker-free LEDs. The artificial lights with the most flicker are flickering LEDs. Note that sometimes misleading marketing misapplies the term "flicker-free" to flickering LEDs. Only "upgrade" school lights from fluorescent lights to LEDs if the LEDs are completely free of all flicker. Installing flickering LEDs will likely be much worse for sensitive individuals than fluorescent lights. Be aware that typical dimming strategies for LED lights introduce flicker, so consider whether dimming is necessary for the project, and if so, ensure that the dimming doesn't introduce any flicker. Be aware that white tunable or color tunable LEDs use flicker to create particular colors. Other than completely flicker-free LEDs that have no flicker, incandescent lights have the least flicker. An article by John Davenport of Energy Focus provides examples of the health an cost benefits of completely flicker-free lighting in schools.

  • Realize that screens are another source of flicker and limiting screen time could be particularly beneficial for sensitive children.

  • I have noticed in my work in schools that some teachers are introducing lamps with household LED light bulbs into their classrooms to provide a more pleasant atmosphere than provided by overhead classroom fluorescent lights. Teachers should be aware that almost all current LED bulbs on the market in the US flicker and teachers who wish to introduce their own light bulbs into the classroom should invest in completely flicker-free LED bulbs.

For allies:

  • Allies can help sensitive individuals by measuring flicker for them (thus allowing the sensitive individual to avoid seeing flicker on a screen themselves) for the purpose of evaluating ambient LED lights and identifying the most flicker-free routes when traveling,

  • Allies can help sensitive individuals to report lights, screen hardware, computer software, or videos to appropriate places, since making such reports generally requires screen use that aggravates sensitive people.

  • Allies can help by acknowledging how severe a problem flicker sensitivity is for some individuals. It can be quite difficult to limit one's normal activities. Showing empathy by helping the affected individual to avoid flicker and to find ways to include the affected individual in activities that do not involve light flicker can be very helpful.

For people struggling with sensitivity to LED lights and/or screens:

  • Please do consult medical professionals. Even if they don't have a test yet to identify what's wrong if the LED lights and/or screens are the only problem, they will be able to do the appropriate tests to rule out other serious medical conditions that might have some similar symptoms.

  • Please do consult professionals who can provide support for any mental health issues.

  • This website should not be viewed as providing medical advice. However, one could point medical professionals unaware of these issues to this website as a starting point to learn more.

  • Along with forums like, these survey results can be used as a reference to show that other people are having similar experiences.

  • Try to report your health problems to the appropriate government agencies in your country and even if you are not in the US, please report your health problems to the United States Food and Drug Administration. In the US, the most important agency to report your health problems with LED lights or LED screens is the FDA, the agency that regulates devices that emit radiation, including visible light: How to report health problems with LED lights or LED screens to the FDA. The FDA Center for Devices and Radiological Health regulates light-emitting devices in the US. Specific lights/LED devices that cause health effects can be also be reported to the US Consumer Product Safety Commission which will transmit your report to the manufacturer. However realize that these reports should also be made separately to the FDA because my experience has been that they are not forwarded from the CPSC to the FDA automatically and as of August 2022, manufacturers receiving CPSC reports have not relayed those reports to the FDA themselves. Our reporting to the FDA is a key step in generating enough data points about this problem in order to motivate further action, such as regulations or funding for scientific research. In the US, health problems from lights/screens in the workplace can be reported to OSHA, the Occupational Safety and Health Administration which can help if employers do not provide accommodations. Note that OSHA is has not to date been aware of the FDA reporting avenue. In the US, The National Institute for Occupational Safety and Health (NIOSH), a division of the CDC, can also be contacted and can evaluate workplace safety. I have also tried reporting to the EPA, but they directed me to the FDA. I have also (unsuccessfully) tried reporting to the NYC Health Department and to the NYC Department of Buildings, but continuing to contact local agencies could also be helpful.

  • Advocate with policy makers for light and screen safety and accessibility regulations.