The Ultraviolet Index Factor is a measure of the intensity of ultraviolet radiation from the sun. It is calculated by measuring the amount of OZONE in the atmosphere, which is a gas that absorbs UV radiation. OZONE is typically measured in Dobson Units (DU), and the Ultraviolet Index Factor is calculated by dividing the DU by 40. The Ultraviolet Index Factor is used to determine the risk of sunburn and other skin damage due to exposure to UV radiation.