For a long time we have been told to beware of the sun-rays and protect ourselves from the impact of sun rays upon our skin. The truth is probably not as bad and simple. Sunlight gives both benefits, and effects harm by exaggerated exposure.
The effects of sunlight upon the skin are due to the ultra-violet light. These light rays are generally divided in three kinds according to wavelength, UVA with longest wavelength and lest energy in each light quantum, UVB of shorter wavelength, and UVC of shortest wavelength and highest energy.