The longer the wavelength of light, the deeper the penetration of the light into the skin. Ultraviolet light is generally divided into ultraviolet C (200 to 280 nanometers), ultraviolet B (280 to 320 nanometers), and ultraviolet A (320 to 400 nanometers). Of the light that reaches the surface, ultraviolet B (mid-wavelength ultraviolet light) appears to be the most carcinogenic.
