for an example of "marker lights" or "hazard navigation lighting", see:

"Federal Aviation Administration (FAA) guidelines for marking and lighting wind energy
facilities require lights that flash white during the day and at twilight and red at night (FAA
2007). The white daytime lights may be omitted if the turbines are painted white. White light
strobes could be used optionally. All marker lights within a wind farm are also required to flash
simultaneously (approximately 24 times/minute); however, only the perimeter turbines of a
wind farm need such markings, provided that there is no unlighted gap greater than 0.81 km
(0.5 mi). The maximum visibility distance assessment included identifying the maximum
distance at which the red flashing turbine lights were visible at night, on the basis of
observations of the Cedar Creek wind facility.

…

The maximum distance at which the red flashing hazard navigation lighting was officially
recorded as visible in this study was 58.3 km (36.2 mi), on October 16, 2011, at 6:35 PM, for an
observation of the Cedar Creek wind facility made from Chalk Bluff Rd. (SOP #431), southeast
of Cheyenne and northwest of the Cedar Creek facility. The lights appeared as a distant row of
flashing lights visible through foreground obstructions. The lights were not as bright as many
foreground lights, but were not judged to be close to the limit of visibility, and in the authors’
judgment would likely be visible for longer distances; however, topography prevented viewing
the facility from a greater distance. The slow, synchronized red flashing of the row of lights was
obvious, even though the lights were not bright."

("Wind Turbine Visibility and Visual Impact Threshold Distances in Western Landscapes": http://is.gd/NWI9ZI )