Ultraviolet (UV) radiation in sunlight is the most prominent and ubiquitous physical factor in our natural environment responsible both for photoaging of the skin and for developing skin cancer. The sun-seeking habits in our populations contributed strongly both to the increase in skin cancer observed in the last two decades and to photodamage. It is highly recommended for both children over the age of six months and grown-ups to use effective sunscreen under exposure for UV radiation. At the same time it is important to achieve sufficient UV stimulation in the skin for production of vitamin D. Vitamin is essential for absorption of calcium from the gut and plays very important role for bone health. Effective and reliable measure of UV index under sun exposure is therefore important tool to obtain enough UV stimulation in the skin for synthesis of vitamin D but on the same time to avoid sunburn.