A preliminary study into minimising the use of warning lights on wind turbines in Germany -- a potential source of disturbance to local communities, but an essential air traffic safety requirement -- has found that using the transponder signals emitted by aircraft at night to trigger turbine lights when needed could provide a solution. A test experiment on turbines near the federal police air station at Fuhlendorf in Schleswig-Holstein proved successful, says the study published by Germany's federal wind energy association, Bundesverband Windenergie. The method, however, is only useful in areas where use of transponders on aircraft is mandatory, notes the study. A second experiment at a 12-turbine wind farm in Uckermark in east Germany proved less successful. Here, a radar instrument to pick up on approaching aircraft and trigger the switch-on of lights was placed in the centre of the wind farm. But the movement of the turbine blades disturbed the radar's ability to recognise approaching aircraft at all. The study says further investigations, including use of radar on the periphery of wind farms, are required.