Shadow flicker is the flickering effect caused when rotating wind turbine blades periodically cast shadows through constrained openings such as the windows of neighbouring properties.
The scale of the problem depends on a number of factors such as wind speed and direction, the position and point of the sun and cloudiness.
It can be worse when the sun is low in the sky, at sunrise or sunset, or during the winter, which is also when there are faster wind speeds.
A report by the Department for Energy and Climate Change found that frequency of the flickering caused by the wind turbine rotation is such that it should not cause a significant risk to health.
However it cited one study that found in the long term it could “significant nuisance”. Campaigners claim that flicker causes extreme stress to people and can cause headaches.
There are also concerns that flicker causes a problem with certain grazing animals. It is claimed it can “spook” horses.
The researchers only identified one case of shadow flicker in the UK and therefore concluded that there have not been extensive issues with it.
In the few cases where problems have arisen, they have been resolved effectively using mitigation measures, in particular turbine shut down systems. Also growing vegetation to stop the shadow, installing blinds or shutters or changing the position of the wind turbine.
The report concluded that developers should not build wind turbines too close to human dwellings and action should be taken where flicker is caused more than 30 hours a year.
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