Subjectivity of flicker
Computer CRT displays usually operate at a vertical scan rate well over 60 Hz (modern ones are around 100Hz), and can thus be considered flicker-free. Other display technologies do not flicker noticeably so the frame rate is less important. LCD flat panels do not seem to flicker at all as the backlight of the screen operates at a very high frequency of nearly 200 Hz, and each pixel is changed on a scan rather than briefly turning on and then off as in CRT displays. In some cases, it is possible to indirectly detect flicker at rates well beyond 60 Hz in the case of high-speed motion, via the stroboscopic effect. Human factors experts refer to this effect as a Phantom Array. Fast-moving flickering objects zooming across view (either by object motion, or by eye motion such as rolling eyes), can cause a dotted or multicolored blur instead of a continuous blur. A common example of this phenomenon is the DLP Rainbow Effect. Some special effects, such as certain kinds of electronic glowsticks commonly seen at outdoor events, have the appearance of a solid color when motionless but produce a multicolored or dotted blur when waved about in motion.
Fluorescent lamps using conventional magnetic ballasts flicker at twice the supply frequency. Electronic ballasts do not produce light flicker, since the phosphor persistence is longer than a half cycle of the higher operation frequency. The 100–120 Hz flicker produced by magnetic ballasts is associated with headaches and eyestrain.[2] Individuals with high critical flicker fusion threshold are particularly affected by magnetic ballasts: their EEG alpha waves are markedly attenuated and they perform office tasks with greater speed and decreased accuracy. The problems are not observed with electronic ballasts.[3] Ordinary people have better reading performance using high-frequency (20–60 kHz) electronic ballasts than magnetic ballasts.[4]
The flicker of fluorescent lamps, even with magnetic ballasts, is so rapid that it is unlikely to present a hazard to individuals with epilepsy.[5] Early studies suspected a relationship between the flickering of fluorescent lamps with magnetic ballasts and repetitive movement in autistic children.[6] However, these studies had interpretive problems[7] and have not been replicated.
http://en.wikipedia.org/wiki/Flicker_fusion_threshold