Unanswered questions in biomedical flicker research

What isn't yet known about the health effects of flicker in the scientific literature?

To my knowledge, there is not yet evidence in the research literature to answer these questions:


Lighting experts have been asking for help from the neurological community. In 2015 while developing the first LED flicker guidelines, the IEEE international committee of experts on flicker recognized the absence of relevant direct research on the biological effects of LED flicker, and urged

In fact, an additional purpose of this document is to urge industry and research laboratories to continue to critically evaluate data from research and from field experience and make additional recommendations when supported by data. The risk analysis discussion in Clause 7 should allow research entities to identify areas of valuable research topics that could further the understanding of the human biological effects of light flicker.”(IEEE std 1789, 2015, Section 1.3).

As recently as July 2019, LED flicker expert Naomi Miller from Pacific Northwest National Laboratory (PNNL) urged for research on the biological effects of LED flicker to begin and she offered the collaboration of PNNL with the neurological community during a talk for the Illuminating Engineering Society (Naomi Miller. Metrics in Motion: Flicker and Glare. July 11, 2019 webinar, minute 59 and as her final message in minute 111). She also said in reference to the problem with a recently-developed, more relaxed flicker metric than the IEEE recommendations, SVM, being based only on the average observer rather than sensitive individuals, “Recent work has shown that 25% of people are more sensitive than other people and these tend to be the people that suffer some of the worst effects such as migraines and headaches” (minute 57).


Is LED sensitivity a larger problem than is currently apparent to the medical community?

LED sensitivity is a relatively new problem since LEDs are new and symptoms of sensitivity may not overlap completely with previously-described conditions.

There is a hint in a recent large-scale public health study that there may be a new, common class of headache with light sensitivity that doesn't clearly fit prior headache diagnostic criteria (Li et al., 2020, discussed in Background: Health Effects of ≥100 Hz flicker).

There are many reasons why LED flicker might currently be under-reported to neurologists or other medical professionals as a trigger of adverse health outcomes:

Since a patient's first significant symptom onset might begin when exposed to LED lights at a new or recently-remodeled building, the possibility that some other aspect of the construction process might be triggering symptoms might further delay identification of the cause.

Even if patients report LED sensitivity to neurologists, ophthalmologists, optometrists or other medical professionals, there is a historical bias in the medical community to downplay the potential seriousness of even traumatic injury to the brain, such as in concussion, so it would not be unreasonable to expect it to be even more likely for medical professionals not to recognize the potential seriousness of injury to the nervous system via light, which of course does not involve any physical contact. The absence of objective biomarkers of nervous system or neuroinflammatory changes (other than upon autopsy) in post-concussion syndrome or for the photophobia experienced in migraine or dry eye disease raises the likely possibility that there also may not be readily measurable, objective biomarkers to diagnose sensitivity to LED flicker or to detect potential nervous system or inflammatory signalling.

Further complicating matters for patients is another long-standing bias in the medical community to believe that photophobia, sensitivity to light, has a purely psychological, rather than physiological basis. Even through research in recent years has demonstrated the physiological basis of photophobia syndromes, there may still be difficulties for patients. Medical professionals might still think that the "sunglasses sign," wearing tinted glasses in the clinic, is a sign of a purely psychiatric disorder or a sign that the patient has made up the symptoms to seek attention, rather than evidence that the light in the clinic is having a genuine impact on the patient's physical health. Howard & Valori (1989), describe clinician's use of the sunglasses sign, as an indicator that a patient does not have a physiological condition, as a long-standing, widespread assumption in clinical practice that had not been validated by evidence. The preponderance of currently-available evidence suggests that there are physiological causes of photophobia and that the vast majority of patients exhibiting the sunglasses sign have photophobia with a genuine physiological basis (reviewed in Digre and Brennan, 2012 and Katz and Digre, 2016). 

Thus, even though the biological safety of LED light flicker was questioned during the development of this technology, no relevant tests of the safety of LED light flicker were done prior to the mass public rollout of the technology. The public has been unknowingly exposed to light flicker without any clear path for recognizing or reporting symptoms, and in the context of a medical system that has not been primed to recognize potential symptoms or to understand that despite historic clinical biases, patients reporting symptoms should be taken seriously. Despite having the ability to manufacture safe, flicker-free LED lights, manufacturers have largely chosen not to do so in recent years and have at the same time adopted language and marketing practices that have the effect of concealing the presence of flicker in their lights.

The goal of this website is to begin to focus research attention, regulatory attention, and public attention on the potential health impacts of LED light flicker and the complex forms of flicker on device screens. The hope is also that lighting manufacturers, computer hardware and software designers, and video creators will voluntarily take action to remove both obviously visible flicker and hidden flicker from their products.