In the United States, incandescent and fluorescent lamps go on and off 60 times per second because of the cycle of electricity. About 1 percent of the population in the United States can actually see these 60Hz (60 Hertz) cycles in lamps. In Europe they use 50Hz, and a somewhat higher percentage can see what has been called a "flicker."
Lamp flicker has, in the past, been associated with some forms of seizures.
Today, however, newer fluorescent lamps cycle at 23,000Hz, and no one can see the flicker. The brain cannot be aware of something that changes that quickly. Thus if there were an epileptic relationship under old style fluorescent light ballasts, then it would be completely eliminated at the electronic ballast higher frequencies.
Sources on "flicker" and its effects on health
Flicker can be unhealthy. It causes seizures in about 4 percent of patients with epilepsy.
Jeavons, P.M. and Harding, G.F.A. (1972). Photosensitive Epilepsy. A Review of the Literature and a Study of 460 patients. William Heinemann Books, London. 121pp.
Some photosensitive patients may induce their seizures by slow eye closure.
Binnie, C.D., Darby, C.E., de Korte, R.A. and Wilkins, A.J. (1980). Self-induction of epileptic seizures by eye closure: incidence and recognition. Journal of Neurology, Neurosurgery and Psychiatry, 43, 386-389.
Wastell, D.G., Wilkins, A.J. and Darby, C.E. (1982). Self-induction of epileptic seizures by eye closure: Spectral analysis of concomitant EEG. Journal of Neurology, Neurosurgery and Psychiatry, 45, 1151-1152.
Television flickers. The lines that make up the picture are refreshed 25 times per second, and the whole screen flashes 50 times per second. Both sources of flicker can cause seizures.
Wilkins, A.J., Darby, C.E., Stefansson, S.F., Jeavons, P.M. and Harding, G.F.A. (1979). Television epilepsy: the role of pattern. Electroencephalography and clinical Neurophysiology, 47, 163-171.
Certain visual display units can cause seizures for this reason.
Wilkins, A.J. (1987). Photosensitive epilepsy and visual display units. In E. Ross, D. Chadwick and R. Crawford (ed.), Epilepsy in Young People. Chichester: John Wiley, pp. 147-155.
Flicker is not perceptible at frequencies of about 100 flashes per second, but it nevertheless affects the firing of cells in the retina and subcortical structures.
Berman, S.M., Greenhouse, D.S., Bailey. I.L., Clear, R.and Raasch, T.W. (1990). Human electroretinogram responses to video displays, fluorescent lighting and other high frequency sources. Optometry and Vision Science 68(8), 645-662.
Eysel U.T. Burandt U. (1984). Fluorescent light evokes flicker responses in visual neurones, Vision Research, 24(9), pp. 943-948.
The rapid imperceptible flicker from visual display terminals and fluorescent lighting affects eye movements.
Wilkins, A.J. (1986). Intermittent illumination from visual display units and fluorescent lighting affects movements of the eyes across text. Human Factors, 28(1), 75-81.
Fluorescent lighting causes eye-strain and headaches.
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.
People with agoraphobia can be sensitive to light. Their heart rate is increased when fluorescent lighting flickers imperceptibly.
Watts, F.N. and Wilkins, A.J. (1989). The role of provocative visual stimuli in agoraphobia. Psychological Medicine, 19, 875-885.
Hazell, J. and Wilkins A.J. (1990). A contribution of fluorescent lighting to agoraphobia. Psychological Medicine 20, 591-596.
Warm white lamps flicker least. Fluorescent lamps controlled by high-frequency circuitry have very little flicker.
Wilkins, A.J. and Clark C. (1990). Modulation from fluorescent lamps. Lighting Research and Technology 22(2), 103-109.
With most fluorescent lamps the rapid imperceptible flicker is greatest for the blue and green components of white light. Rose-brown glasses therefore reduce the flicker.
Wilkins, A.J. and Wilkinson P. (1991). A tint to reduce eye-strain from fluorescent lighting? Preliminary observations. Ophthalmic and Physiological Optics, 11, 172-175.
The glasses may sometimes prevent headaches in people who use visual display terminals under fluorescent lighting and in children suffering from migraine.
Good P.A., Taylor R.H. and Mortimer M.J. (1991). The use of tinted glasses in childhood migraine. Headache, 31, 533-536.