OCAS uses a low power ground-based radar to provide detection and tracking of an aircraft's proximity to an obstacle such as high buildings, power line crossings, telecom towers or wind turbines.
This capability allows the visual warning lights to remain passive until an aircraft is detected and known to be tracking on an unsafe heading.
[1] The OCAS system is designed to protect obstacles that are vulnerable to low flying aircraft.
OCAS detects the ground speed, heading and altitude of approaching aircraft and determines whether it will adequately clear the obstacle.
This capability allows the lighting system to remain passive (in the off position) the vast majority of the time thus preserving the dark sky environment while adhering to strict safety standards set out by the FAA.