The invention relates to a field of outdoor (street) illumination, in particular, to methods of controlling light emission, as well as to a field of optical devices, in particular, to methods of reducing light pollution that affects astronomical instruments. The method of reducing impact of light of outdoor illumination devices on astronomical instruments consists in generating a light flow of illumination devices in a form of periodical pulses and in blocking the light flow directed to a light-sensitive matrix of an astronomical instrument during arrival of the light flow pulses of the outdoor illumination devices. Thus, light pollution of astronomical instruments by outdoor illumination devices is avoided.