Shadow control of wind turbines

A shadow-control system of a wind turbine, the wind turbine having a rotor that, when rotating and when the sun is at a certain position, may cast an intermittent shadow onto an object in the vicinity of the turbine, the shadow-control system being arranged to cause the wind turbine to be stopped, based on a shadow-related shut-down condition, so that intermittent shadow is not cast onto the object, wherein the shut-down condition comprises a result of a comparison between a direct-light intensity and an indirect-light intensity being beyond a first direct-to-indirect light threshold, wherein the shadow-control system comprises:

• an eastward-oriented light sensor;
• and
• a westward-oriented light sensor, the light sensors provide measured direct- and indirect-light intensities for the comparison, the light sensors being able to measure the direct-light intensity when irradiated by the sun and the indirect-light intensity when not irradiated by the sun, and wherein the shadow-control system has a hysteresis in operation such that a light-measurement result below the first direct-to-indirect light threshold is not sufficient to cause the operation to be resumed.