ZAGREB, July 1, 2018 - The light pollution of the sky above Zagreb, a result of the use of artificial light, is 16.9 magnitudes on average, and is bigger than the sky's light pollution in Hong Kong, according to survey findings published by the Faculty of Mining, Geology and Petroleum Engineering in Zagreb.

Professor Željko Andreić gauged the brightness of the sky above the faculty's building near downtown Zagreb for six years and established that the average brightness of the night sky was approximately constant, with annual differences caused by changes in weather.

Night minimums, maximums and medians of sky brightness change considerably due to weather conditions, often between two and three magnitudes, according to the findings.

Clear nights have less while cloudy nights have more light pollution, with sky brightness being about 15 magnitudes on clear nights and about 18.2 on cloudy nights, Andreić says. Both readings are a little lower in spring and summer.

Compared with Vienna and Hong Kong, Zagreb produces disproportionately high light pollution, Andreić says. In Vienna, which has a population of about 1.7 million, the average brightness of the night sky is between 16.3 and 19.1 magnitudes.

A cloudy night sky in Zagreb is 1.3 magnitudes brighter, or approximately 3.2 more times, than in Vienna, while a clear night sky is 0.9 magnitudes brighter, or about 2.3 more times, Andreić says, adding that Hong Kong, which has an almost nine times bigger population, causes less light pollution than Zagreb.

Night light stops the production of melatonin, a hormone important for human health, causing a higher incidence of breast, prostate and colon cancer, as well as sleeping disorders and depression.