Intensity of light pollution and its impact on phenological phases of trees

The work evaluates the intensity of light pollution in two towns of Central Slovakia from September 2013 to April 2014. Under different weather conditions we performed 20 measurements at 7 sites with the instrument of Lux Meter Velleman DVM 1300 during night hours. We found the relationship between the actual weather conditions and measured values. In comparison with STN EN 12464-2, the valid norm of Slovakia, the threshold of 5 lux was exceeded at 5 observed sites by 1.3-10.4 lux. Some trees react to strong light sources. Intensive night lighting caused the visible delay of autumn phenological phase of leaf colouring on some crown parts of several trees.