Light pollution is any change in the level of natural light in nighttime conditions. It is caused by emissions from artificial light sources. Everything that radiates unnecessarily towards the sky or to the side, and not towards the ground, pollutes the environment and the sky with excess light. Such pollution is harmful for people, animals, environment and negatively effects economy. Research has shown that during the sleep people need complete darkness, otherwise our body does not secrete enough of the hormone called melatonin, which is essential for our immune system and for the fight against stress. To determine light pollution, measurements were made at nine different locations in three counties, in order to classify the quality of the sky and the effects of cities, advertising screens and landscape lighting on the night sky. The highest level of measured light pollution was near the advertisement screen in Stubičke Toplice (10,62 mag/arcsec2), while the lowest was at the Trakošćan castle (19,45 mag/arcsec2). To lower the light pollution, public education about negative effect on the living world and reasonable usage of light energy is necessary.