Visual marking of wind turbines

Development of wind turbines and windfarms is taking place in full force in Norway today. In this connection, the topic of visual light pollution is highly relevant. The Norwegian Civil Aviation Authority (CAA-N) notices an increased demand of requests and applications for radar control of obstacle lights at windfarms. The role of the CAA-N is to ensure aviation safety.

If we look at the regulation, this opens up for use of systems activated by aircrafts, for example radar control of obstacle lights. Related to this increased demand, the CAA-N needs, internally in our organization and with external agencies, to clarify a number of issues related to any potential accept of radar control of obstacle lights in windfarms. A clarification is expected to be available no earlier than the first half of 2021.

In the meantime, concessionaries can relate to the clear and detailed requirements for visual marking of wind turbines and windfarms that exist.

  • The owner of an aviation obstacle is responsible for ensuring that the requirements of the regulations are met (BSL E 2-1 § 2). Anyone who does not fulfill his obligations may be fined in accordance with the Civil Aviation Act § 13a-5 (cf. BSL E 2-1 § 22)
  • No later than 30 days before the construction of a wind turbine or windfarm is initiated, this must be reported to the Norwegian Mapping Authority (BSL E 2-1 § 4) Information at the Mapping Authority and registration can be done here.
  • Requirements are set for reporting accuracy when registering with the Norwegian Mapping Authority (BSL E 2-1 § 5)
  • The obligation applies to all aviation obstacles with a height of 60 meters or more, and all aviation obstacles must be marked visually (BSL E 2-1 § 7)


CAA-N comments: the obligation to mark with obstacle lights also applies to wind turbines where the tower is under construction and has reached a height of 60 meters or more. The concessionaries (owner, developer or contractor) needs to find solutions on how to mark the wind turbine(s) temporarily and until the windfarm is completed with permanent obstacle lights connected to electricity. There are portable solutions, obstacle lights that run on batteries, solar cells or fuel cells. CAA-N accepts temporary solutions, but does not accept unmarked obstacles.

  • Wind turbines must be marked with a light color (gray, gray-white or other shades of white, but not snow-white). The color requirement does not apply to the lower third of the tower (BSL E 2-1 §§ 10 and 15)
  • Each wind turbine must have two obstacle lights, located on top of the nacelle. For wind turbines that constitute a windfarm, the CAA-N may approve that only the wind turbines that make up the wind farm's perimeter (outer boundary) are marked. This given that the individual distance between marked wind turbines maintains aviation safety. The CAA-N may stipulate that the center or the highest wind turbine in the windfarm must also be marked. If flashing obstacle lights are used in a windfarm, the flashes must be synchronized (BSL E 2-1 § 10).

CAA-N comments: it is not a given that perimeter marking of a windfarm will be granted. Applications are assessed individually. The assessment emphasizes, among other things; traffic density, flight pattern, nearby landing sites and topography.

  • Requirements for obstacle lights; If LEDs (Light Emitting Diodes) are used, these must emit light with a wavelength that makes the obstacle lights visible to pilots who use night vision goggles (Night Vision imaging System). Obstacle lights must be operational at least 95% of the time, calculated as an average on an annual basis (BSL E 2-1 § 16)
  • Wind turbines with a height of up to 150 meters (up to but not including 150 m), shall be marked with medium intensity obstacle lights type B or C. (BSL E 2-1 § 17 (4))
  • Wind turbines with a height of 150 meters or higher (from and including 150 m or higher), shall be marked with high-intensity obstacle light type B. There is no requirement for light marking at intermediate levels (BSL E 2-1 § 17 (5)).


Height of wind turbine: defined as the vertical distance from the terrain and to the top of the rotor blade, when it is in the highest position.