(i) Ultraviolet-B It is an electromagnetic radiation which has a shorter wavelength than visible light. It is a harmful radiation that comes from sunlight and penetrates through the ozone hole to the earth’s surface. It causes many health hazards in humans. UV-B damages DNA and activates the process of skin ; ageing. It also causes skin darkening and skin cancer. High levels of UV-B cause corneal cataract in human beings.