A small amount of solar radiation is welcome, it is necessary for the synthesis of vitamin D, which promotes absorption of calcium - necessary for building bones. It is also known that seasonal changes (shorter days in winter) for a large number of people can cause fatigue despite sufficient quantity of sleep and loss of energy, lethargy, sadness and anxiety. A group of these symptoms (which may be of different intensity) is called a seasonal depressive disorder and affects about 10% of the population. It is believed that the development of this disorder causes the decrease of sunlight during winter months. The lack of sunlight affects biochemical balance in the brain by changing the mechanism of secretion of melatonin, a hormone important for healthy sleep, and serotonin, which regulates mood. But the last ten years, scientists warn of damage of the ozone layer in the atmosphere, causing an increasing amount of UV rays reaching the Earth's surface, thereby increasing the intensity of solar radiation, with all its negative consequences.