The health effects of lighting flicker are a complex phenomenon that has been studied for some time. The IEEE has proposed the 1789 standard to help prevent potential negative health consequences of both short- and long-term exposure to flickering lights. The proposed standard is extremely conservative in its scope. Under the proposed standard, any light that flickers at or below 200Hz would be considered unhealthy. It would essentially call standard incandescent lighting and AC-powered LED lighting and the majority of HPS lighting as “dangerous to your health”, and claim that such lighting would impose a high risk of negative health effects.
Not surprisingly, organizations are speaking out against the 1789 standard including the National Electrical Manufacturers Association (NEMA), who is directing members to disregard the spec, while there is a separate, very active effort to bring together a like-minded consortium and launch an investigation spearheaded by Once Innovations.
Regardless of whether or not the standard would be bad for the solid state lighting industry, the question remains, does exposure to light flickering below 200Hz cause negative health effects? And the second part to that question is whether or not the 200Hz standard is warranted given what we know about these potential health effects?
We have numerous articles about the health effects of flickering light. From what we’ve examined, requiring lighting to flicker at 200Hz or greater seems not just conservative, but ludicrously conservative. While there are some health effects, those that have been documented and studied occur significantly below 200Hz. All of the negative effects occur below 120Hz, and most occur below 60Hz.
Back in 2010 the IEEE published a relatively comprehensive literature review of the health effects of flickering light. The health effects can be categorized as immediate or long term (Wilkens et al. 2010).
Two studies found that the human retina can resolve light modulation in the frequency range 100-160Hz and even up to 200 Hz although the flicker is too rapid to be consciously noticed. (Burns et al. 1992, Berman et al., 1991). These studies which looked at EEG readings imply that the human retina (the optic nerves themselves) cannot detect flickering light (even subliminally) in even the most sensitive of individuals much beyond 200Hz. So, not only does modulation above 200 Hz have no negative health effects, it apparently causes no effects at all through known mechanisms in even the most sensitive individuals, suggesting that the 200Hz standard is, at the least, overly-conservative.
Among the most serious negative health effects documented related to lighting flicker have to do with an extremely small portion of the population who are photosensitive epileptics. The IEEE paper notes that photosensitive epileptics make up about 1 out of every 4000 people. Among photosensitive epileptics, light flicker below about 70Hz could induced seizures for a small percentage of the photosensitive epileptics. At 65 Hz, only about three percent of the photosensitive epileptics had seizures. This population is very small with at most about 12 people out of about 400000. Extended to 120 Hz, the number would appear to be pretty much zero.
Other potential health concerns do occur at somewhat higher flicker frequencies. However, these are significantly less serious in nature. Eyestrain and more frequent headaches among headache-prone individuals have been documented at 100Hz. (Wilkens, 1989). Other effects such as eyestrain were also observed at 100Hz. Again this was among a very small minority of people.(Wilkens, 1989).
Additional potential effects were not technically health-related but were productivity related. Visual tasks such as searching were shown to be impaired at 100Hz among certain people (Jaen et al., 2005). While these effects are worrisome, they are far from serious, and only a minority of people suffer from them. Furthermore, these health effects occur far below the 200Hz standard. So, the 1789 standard that the IEEE wants to impose seems far from warranted when you look at documented health effects of lighting flicker.
Berman, S.M., Greenhouse, D.S., Bailey, I.L., Clear, R.D., and Raasch, T.W. (1991) Human electroretinogram responses to video displays, fluorescent lighting, and other high frequency sources. Optom Vis Sci., 68(8),645-62.
Burns, S.A., Elsner, A.E., and Kreitz, M.R. (1992) Analysis of nonlinearities in the flicker ERG. Optom Vis Sci.,69(2), 95-105.
Jaen, M., Sandoval, J., Colombo, E., and Troscianko, T. (2005) Office workers visual performance and temporal modulation of fluorescent lighting, Leukos, 1(4), 27-46.
Wilkins, A.J., Veitch, J.A., Lehman, B. (2010) LED Lighting Flicker and Potential Health Concerns: IEEE Standard PAR1789 Update. Energy Conversion Congress and Exposition (ECCE), 2010 IEEE, 171-178.
Wilkins, A.J., Nimmo-Smith, I.M., Slater, A. and Bedocs, L. (1989) Fluorescent lighting, headaches and eye-strain. Lighting Research and Technology, 21(1), 11-18.