Obstruction lighting, although it is not always used to mark objects at an airport, is classified as aeronautical lighting. It is used for safety and prevents an aircraft from colliding with high constructions and buildings.
Lights used for marking an obstruction can be of different intensity. With regard to that matter, they can be divided into A, B and C type. Type-A light is white, Type-B - red (flashing) and Type-C – also red but constant. ICAO regulations say that high-intensity light can be used instead of painted markings. If an obstruction is not taller than 45 meters, low-intensity lights are used. Type-A lights are used when Type-B lights could blind a pilot. Type-B lights can also occur in a version with two lights and a day/night detector, and a malfunction detector. In turn, middle-intensity lights are used to mark massive obstructions and those which are taller than 45 meters.