Ultraviolet rays

Ultraviolet rays, invisible light lying beyond the violet end of the spectrum. It is produced naturally by the sun and lightning. Prolonged exposure to the sun's ultraviolet rays can result in sunburn and over a period of years, can cause skin cancer. Plants and animals are partially protected from the sun's ultraviolet rays by ozone, a form of oxygen formed in the upper atmosphere. Ultraviolet rays can, however, be beneficial. They are used by physicians to destroy some bacteria and viruses and by food manufacturers to disinfect food containers. Special lamps that produce ultraviolet rays have been successfully used to treat acne and other skin disorders.