Wind turbine light polution
Being tall structures which offer a very real threat to aircraft in flight, there are strict regulations in every country concerning the placing of flashing warning lights on wind turbines. When twind turbines are placed in arrays, as is usually the case with wind farms, the flashing must be synchronised. The lights are powerful enough to be highly visible form a considerable distance, and have been identified as a frequent and common source of irritation to people living within visual range. In the case of Kythera, where proposed wind turbines will be placed in long arrays along the crests of hills and mountains, it will be impossible to escape them by day or by night.
“Significant differences can be noticed between the national regulations of states in Northwest Europe (the Netherlands, Belgium, Germany, France, UK, Denmark, Norway, Sweden and Finland) and North America (Canada and the US). Some states, such as the US, UK, Belgium, Germany and Denmark, pose that the visibility of wind turbines during the daylight period is sufficiently guaranteed by the prescribed marking. In these states obstacle lights are not required during the daylight period. It should be noted however, that in Belgium and Germany the marking requirements are stricter. In addition to the white painting of the turbine, these states require orange or red bands on the turbine blades, mast and nacelle. Obstacle lights can be used as an alternative.
On the contrary, other states, like France and the Scandinavian countries, prescribe high-intensity lights (100,000cd-200,000cd) for the daylight period.
There are also notable differences in the prescribed intensity at night. Requirements vary between 100cd (Belgium and Germany) and 100,000cd (Denmark). Belgium and Germany even allow the use of low-intensity lights (10cd) when installed at the blade tips. Most states require wind farms to be fitted with synchronously flashing lights. Perimeter lighting is also allowed in these states, provided the spacing does not exceed the ICAO norm of 900m. The option to deviate from this norm based on a dedicated study, as allowed by Annex 14, is generally not adopted. The exception to this is the UK, which allows the use of steady lights (ICAO Type C) to reduce residential annoyance. However, perimeter lighting is not permitted in the UK, i.e. all (onshore) wind turbines have to be fitted with obstacle lights.”
Source: Netherlands Aerospace Centre, “Obstacle Lighting of Onshore Wind Turbines”, 2016. Full document: https://www.nlr.org/wp-content/uploads/2018/02/Obstacle-Lighting-of-Onshore-Wind-Turbines.pdf
Further reading: https://www.itl-llc.com/lighting-guide/windfarm