Low-frequency flicker (1–70 Hz) has been shown to be more detrimental than flicker at higher frequencies (> 70 Hz). Typically, the highest flicker frequency that a person can detect is 60–90 Hz. The most common 100 Hz flicker cannot be detected by a human being. ERG (electroretinogram) responses indicate that invisible flicker passes through the retina at frequencies as high as 200 Hz (Berman et al., 1991). Studies have shown that flickering light may have detrimental effects on some people’s health. Even natural flickering light has been proven to increase the risk of getting an epileptic seizure or a migraine attack in a person with such a tendency.
Studies have shown that flickering light may impair concentration or cause tiredness, a feeling of sickness, sore eyes (2), or a drop in cognitive performance (3, 10). These can be considered mild symptoms caused by flickering light, but they can affect anyone. Studies have indicated, for example, that fluorescent lamps normally flickering at 100 Hz may cause headaches and sore eyes (2).
...FOR SOMEONE WHO SUFFERS FROM MIGRAINE
About 5–10% of all people in the world suffer from migraine. A migraine attack triggered by flickering light can be considered a more serious harm than the mild symptoms listed above. According to studies, in about 38% of people who suffer from migraine, the attack is triggered by light (6).
People who suffer from migraine are sensitive to visible light and particularly to its periodic fluctuation—called flicker—and find it unpleasant (7).
In studies where test subjects were exposed to flicker, it was found that people who did not suffer from migraine gradually adapted to flicker or became less sensitive to bright and flickering light. On the other hand, those who suffered from migraine became more sensitive to flicker even though the test was conducted at a time when they did not have a headache (8).
...FOR SOMEONE WHO SUFFERS FROM EPILEPTIC SEIZURES
Although only about 1% of all people in the world suffer from epilepsy, it can be considered one of the most serious health harms that flickering light may cause. One study (1) showed that in EEG measurements, persons sensitive to light presented epilepsy-like responses when the flicker frequency was in the range of 1–65 Hz. A flicker frequency in the range of 15–25 Hz was especially provocative and caused epileptic EEG changes in a majority of the test subjects. Flickering light may cause 2–14% of epilepsy patients to get an epileptic seizure.
(1) Summary of visually induced epileptic seizures and background material from various studies: Photic- and pattern-induced seizures: a Review for the Epilepsy Foundation of America Working Group by Robert S. Fisher 1, Graham Harding 2, Giuseppe Erba 3, Gregory L. Barkley 4, Arnold Wilkins 5
(2) Fluorescent lighting, headaches and eyestrain. AJ Wilkins, I Nimmo-Smith, A I Slater and L Bedocs, Lighting Res. Technol. 21(1) 11-18 1989
(3) Visual Task Performance and Perceptions of Lighting Quality Under Flickering Illumination. Light & Vis. Env. Vol.37, No.4, 2013 (John D. BULLOUGH, Nicholas P. SKINNER and Kathryn SWEATER HICKCOX, J)
(4) LED Lighting Flicker and Potential Health Concerns: IEEE Standard PAR1789 Update, (Arnold Wilkins, Jennifer Veich and Brad Lehman)
(5) PROPOSING MEASURES OF FLICKER IN THE LOW FREQUENCIES FOR LIGHTING APPLICATIONS, Brad Lehman, Arnold Wilkins, Sam Berman, Michael Poplawski, Naomi Johnson Miller
(6) The triggers or precipitants of the acute migraine attack, L Kelman. Cephalalgia 2007; 27:394-402
(7) Detection and discrimination of flicker contrast in migraine, Oliver Haranovic, Mechel Thabet, Hugh R Wilson and Frances Wilkon, Cephalalgia 2010
(8) The locus of flicker adaptation in the migraine visual system: A dichoptic study, Michel Thabet, Frances Wilkinson, Hugh RWilson and Olivera Karanovic, Cephalalgia 2012
(9) Human Electroretinogram Responses to Video Displays, Fluorescent Lighting, and Other High Frequency Sources, Samuel Berman, Daniel Greenhouse, Ian Bailey, Ropert Clear, Thomas Raasch, Optometry and Vision Science 1991, Vol.68, No. 8, pp. 645-662
(10) The impact of flicker from fluorescent lighting on well-being, performance and physiological arousal, Rikard Kuller & Thorbjorn Laike, Ergonomics 1998, 41:4, 433-447