Wind turbine aircraft obstruction markings such as white and red flashlights play an important role for the social acceptance of wind farms. Actually, some residents complained about these flashes. So far, empirical evidence is lacking whether to categorize obstruction markings as substantial or minor annoyance. The overall aim of the study was to provide insight into the impact of obstruction markings on residents living in the vicinity of wind farms. Additionally, recommendations for administrations and the wind industry to apply obstruction markings are derived. To test the obstruction marking’s impact a survey was conducted including 15 wind farms throughout Germany. Per wind farm condition at least 30 residents living in its proximity completed a standardized questionnaire. The questionnaire was related to environmental, stress and social psychological aspects e. g. annoyance, psychic and somatic complaints, behaviour and coping. Also, the impacts of moderating factors were included like attitudes towards the wind farm, chronic diseases, sensitivity to light or occupancy. As possible determinants of annoyance and stress effects, the following characteristics of the obstruction markings and the wind farms themselves were taken into account: (1) Different types of day obstruction markings: In Germany LED, Xenon-lights, and redwhite- red-markings on blades are allowed. (2) Night obstruction markings: In Germany red flashlights are used during the night. The impact of day and night obstruction markings was compared to shed light on possibly differing levels of annoyance. (3) Obstruction markings with and without synchronisation: If the lights are synchronized they flash with the same pulse, if not they flash with different pulses. (4) Obstruction markings of wind farms in simple (plain, low building density) vs. complex (forest, hills, high building density) structured landscapes: The appearance of the whole wind farm depends on the landscape in which the wind farm is embedded. // For reliable comparison, the sample of wind farms chosen for this study had to meet the following criteria: (1) The overall height of the wind turbines has to equal or exceed 100 m, (2) each wind farm has to comprise a minimum of five wind turbines, (3) the sample of wind farms has to contain a minimum of six wind farms with visibility regulation, (4) the wind turbines have to be visible for residents living at a maximum distance of 8 km from the wind farm. // In general, different effects of wind turbine aircraft obstruction markings on residents were found. Further details will be presented. The study was supported by a grant of the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety and the State Office for Agriculture, Environment and Rural Regions, Office Schleswig.