Greg Tucheh, age 14, of Indian Trail, N.C., for his question:
WHAT ARE THE EFFECTS OF ULTRAVIOLET?
Ultraviolet radiation is related to light, radio and other forms of electromagnetic energy. As far as its general behavior is concerned, there is a good side and a not‑so‑good side. Some of its effects are useful and beneficial to living cells. Others are downright dangerous. Its different effects are caused by the wide range of different wavelengths.
The sun emits various forms of electromagnetic energy, pulsing along in different wavelengths at the speed of light. These wavelengths are measured by the angstrom unit. And it takes 100 million of these invisibly small units to measure one centimeter. The rainbow‑colored wavelengths of ordinary light range from about 4,000 to 7,000 angstroms.
The wavelengths of ultraviolet radiation begin at 4,000 angstroms, where the shortest violet waves of light end, and dwindle down to 40. Within this wide range, longer and shorter waves have different effects. The shortest waves have the most penetrating power, enough to cause serious sunburns. However, much of this shortwave radiation is absorbed by the air as it comes down through the atmosphere.
Sunburn is more serious at high altitudes, where there is more short‑wave ultraviolet. But even at sea level, there is enough to cause permanent skin damage when a person is exposed to long hours of suntanning. Other wavelengths help and may be necessary to the chemical activities that go on in living plant cells.
As a rule the longest ultraviolet rays are not absorbed by living tissues. Scientists use those in the 2,000 to 3,000 range to study all sorts of effects in the biochemistry of living cells. These rays do not penetrate deeply, but they can be used to destroy single‑cell organisms. Hence, ultraviolet radiation is used to destroy dangerous bacteria in foods.
In the nonliving world ultraviolet rays affect certain minerals. Its energy is absorbed by their electrons and released as fluorescence. After exposure to ultraviolet, certain minerals glow with their identifying colors.
Ultraviolet passes through a prism made of quartz crystal and reveals colors shorter than the violet rays of ordinary light. In a fluorescent lamp, an electric current produces ultraviolet when it passes through mercury vapor. Various coatings on the inside of the tube absorb this radiation and convert it into different colors of visible light. In some way or other, ultraviolet radiation affects every living and nonliving substance in the world.