Ultraviolet A
One of the three types of invisible light rays (together with ultraviolet B and ultraviolet C) given off by the sun.
Although ultraviolet C is the most dangerous type of ultraviolet light in terms of its potential to harm life on earth, it cannot penetrate earth’s protective ozone layer. Therefore, it poses no threat to human, animal or plant life on earth.
Ultraviolet A and ultraviolet B, on the other hand, do penetrate the ozone layer in attenuated form and reach the surface of the planet. Because ultraviolet A is weaker than ultraviolet B, scientists long blamed ultraviolet B as the sole culprit in causing skin cancer in persons with a history of sunburn and repeated overexposure to ultraviolet radiation. Recent research, however, has also implicated ultraviolet A as a possible cause of skin cancer. In addition to natural light from the sun, artificial light from tanning lamps contains ultraviolet A and ultraviolet B. Electric arc lamps can also generate ultraviolet light to heat furnaces for melting and to enable motion-picture projectors to show movies.
Though ultraviolet light can damage health, it can also maintain or improve health. When ultraviolet light strikes human skin, it triggers the production of vitamin D, which promotes the growth of bones and teeth.
Read Also:
- Ultraviolet B
One of the three types of invisible light rays (together with ultraviolet A and ultraviolet C) given off by the sun. Although ultraviolet C is the most dangerous type of ultraviolet light in terms of its potential to harm life on earth, it cannot penetrate earth’s protective ozone layer. Therefore, it poses no threat to […]
- Ultraviolet C
One of the three types of invisible light rays (together with ultraviolet A and ultraviolet B) given off by the sun. Although ultraviolet C is the most dangerous type of ultraviolet light in terms of its potential to harm life on earth, it cannot penetrate earth’s protective ozone layer. Therefore, it poses no threat to […]
- Ultraviolet radiation
Invisible rays that are part of the energy that comes from the sun. Ultraviolet radiation can burn the skin and cause skin cancer. Ultraviolet radiation is made up of three types of rays — ultraviolet A, ultraviolet B, and ultraviolet C. Although ultraviolet C is the most dangerous type of ultraviolet light in terms of […]
- Umami
The taste of substances such as glutamate and monosodium glutamate (MSG) that are found in foods like bouillon and other stocks. Umami is the fifth primary element of taste. The other four are sweet, sour, salty, and bitter. It was discovered in 1907 by Kikunae Ikeda. Umami is the Japanese word for delicious flavor.
- Umbilical cord
The cord that connects the developing fetus with the placenta while the fetus is in the uterus. The umbilical arteries and vein run within this cord. The umbilical cord is clamped and cut at birth, and its residual tip forms the bellybutton.