UVA rays have an ultraviolet radiation wavelength between 400-320 nanometers. They account for 90-95% of all UV radiation, and are present in daylight hours, in all seasons, and can even penetrate glass. UVA rays go deeper into the epidermis than UVB and are responsible for tanning.
UVB rays have an ultraviolet radiation wavelength between 320-290 nanometers (the shorter the wavelength, the higher the radiation). UVB rays account for only 5-10% of all solar radiation, strongest between the hours of 10am-4pm from April to October, penetrating both clouds and glass. Because of its high radiation wavelength, UVB rays will damage the epidermal layers of the skin without proper UVB protection, causing sunburns.