Derived from the Latin 'ultra', meaning "beyond," Ultraviolet (UV) light has a higher frequency than violet light—the highest frequency of visible light. The spectrum of UV radiation can be subdivided into a number of ranges in nanometers, from 10-400. These subdivisions allow for various applications of UV light in a number of industries, such as health, astronomy, detection and inventory.
Some insects, birds, and some children in laboratory conditions can see UV light. In normal human vision, the eye lens blocks most light in the 300-400 nanometers wavelength range. However, for people with aphakia, (missing lens), UV light comes through as whitish-blue or whitish-violet. Seeing "beyond" can be compared with dogs having the ability to hear "beyond." Whistles produce a sound wave that humans cannot hear, but dogs can.
When the doctor tells you to go outside to get your Vitamin D, he's referring to the UV rays that are responsible for strengthening bones. Yet, too much UV radiation in too short a period of time can cause cellular damage, resulting in sunburn. Sunscreens, or "blockers," include ingredients such as avobenzone and oxybenzone that absorb UV rays. Fortunately, the ozone layer filters out the vast majority of UV radiation, enabling humans and vertebrates to exist in sunny climates.
Artificial sources of the UV spectrum have many effects and uses. For curing polymers in the dental field, scientists developed low-cost LED flashlights that emit specific wavelengths in the UV range. Some skin conditions, such as psoriasis and vitiligo receive ultraviolet radiation treatments. UV lights are applicable in label tracking, barcodes, black lights, extreme ultraviolet lithography, optical sensors for instruments, forensic analysis for drug detection, medical imaging of cells, detection of forged bank notes, and digital printing.
On the home front, a bug zapper can save a back yard picnic from annoying biting bugs. UV light attracts the bugs; high voltage wires near the light do the rest.
Consumers purchase UV lights for tanning lamps, UV-protected sunglasses, reptile aquariums, and as cleaners for air and water systems. Additionally, hospitals and food and drug companies use short wave UV "germicidal" lamps to sterilize surgical equipment and the air, and for disinfecting water supplies. UV lights can be installed in air conditioning systems to prevent the growth of bacteria and mold.
Long exposure to UV light breaks apart molecular bonds and destroys cells. Because microbes and mold must be close to the light source in order to be affected, UV lights are placed near the air conditioning coil and condensation pan. Without UV lights, the coil and pan could provide the perfect setting for microbes to grow. Installing UV lights can help keep your system's evaporator coils germ-free.