Occupying some 90 square miles in one of the world’s busiest shipping lanes, London Array must be marked effectively. With structures so tall that the lowest tip of the blades will be at least 22m above sea level, wind turbines must also comply with the very different requirements of aviation regulations. Confusion can be caused by relatively low power (50 candelas) marine beacons flashing white or yellow to be viewed at or around the horizon being required to share space with 2,000 candelas continuous red aviation lights, requiring up to 45% of their power to extend a few degrees below the horizon. The result is beacons which overlap. A distant marine observer will tend to see the aviation light rather than he marine beacon because it is more powerful and also continuous. For mariners, an uncharted continuous red light is the port navigation light of a vessel under way, whereas the red, fixed light of a marine aid to navigation beacon is always charted. Also, the rotating turbine blades mean that both marine and aviation users will see a flashing red light from certain directions.

Wind is the fastest growing energy source worldwide, expanding at an annual growth rate of 30% for over a decade. Marking them is not only an issue in the UK. The International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA) has also been developing recommendations which are available in their document O-117.