Light pollution is a global problem, as inappropriate installation of public lighting negatively affects living organisms and plants and disrupts their natural behavior. In the introduction, this work deals with the issue of light pollution in the field of energy, astronomy and physiology of plants. It also shows the current state of legislation in this field in Slovakia. In the main part of our work, we dealt with the processing and analysis of the findings on the phenological manifestations of woody plants. The aim of the work was to determine the impact on deciduous trees in selected localities of the city of Zvolen and to propose measures to improve their health conditions. We tried to achieve these goals by monitoring the phenological phases of yellowing and leaf fall on vegetative organs of woody plants on the illuminated and non-illuminated part of the crown. The results of the work are graphical and verbal evaluations of the collected phenological data and their comparison, as well as an analysis of the type of public lighting and its distance from the crown.