“Shadow flicker” occurs when the blades of a large wind turbine pass between the sun and the observer, causing an on-again, off-again shadow to be cast by the blades. The flicker can be annoying when trying to read or watch television. If any effect is experienced, it is generally short-lived due to the moving path of the sun, incidence of cloud cover, and wind-driven angling of the turbine sideways to the sun.
Shadow is precisely calculated to determine whether a flickering will fall on a given location near wind turbines, and for how many hours in a year it will do so (for example, 15 minutes a day for 20 days out of the year). Potential problems can be easily identified using these methods.
There is no connection between shadow flicker and epileptic seizures. The frequency, or the number of times something happens per second, is measured in Hertz (Hz). Shadow flicker from wind turbines has a frequency between 0.5 Hz and 1.25 Hz, which is equivalent to between 1 to approximately 1.25 alternations per second. According to the American Epilepsy Foundation this is well below the range of frequencies that can trigger epileptic seizures, which is 5 to 30 Hz.1
1. Noble Environmental Power
Lawrence Technology University – The Importance of Wind Turbine Shadow Flicker
Epilepsy Foundation - Shedding Light on Photosensitivity,One of Epilepsy’s Most Complex Conditions