| Abstract | Electromagnetic radiation between 380 and 780 nm is detected by cells in the retina (sensation), which sends signals to brain structures. Perception is the process by which the brain interprets sensory information. Modulation in the luminous signal (flicker) is perceived at rates up to as high as 100 Hz, although the average critical flicker frequency is around 60 Hz. Flicker is detected (sensed) at rates up to 200 Hz, meaning that there are neural responses in phase to luminous modulation even at rates that the individual would not report having consciously perceived. A small number of people are at risk for photosensitive epileptic seizures at rates from even a short exposure to 3-70 Hz flicker. Longer exposures to 100-120 Hz flicker lead to headache and eyestrain in some sensitive individuals, but the exact population frequency is unknown. Visual performance is detrimentally affected by 100-120 Hz flicker. These effects are not specific to a light source but do vary as a function of the frequency and amplitude of the luminous modulation, its spectral variation, the adaptation luminance, and the contrast and retinal size of the flickering source. There are many unanswered questions about the health effects of flicker (including flicker from LEDs), which the research community should address; however, it would be prudent for the solid-state lighting community to reduce the luminous modulation of its new products as much as possible now, while they are in their initial development. To do so will facilitate rapid market trust and acceptance of this novel technology. |
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