Comment by dpe82

At first I questioned your assertion, but after reading the most recent FAA AC revision (https://www.faa.gov/documentLibrary/media/Advisory_Circular/...) I found:

13.5.3 In most cases, not all wind turbine units within a wind turbine farm need to be lighted. Obstruction lights should be placed along the perimeter of the wind turbine farm so that there are no unlit separations or gaps more than 1/2 SM (0.80 km) (see Figure A-26). Wind turbines within a grid or cluster should not have an unlighted separation or gap of more than 1 SM (1.61 km) across the interior of a grid or cluster of turbines