UV, or ultraviolet, light is an invisible form of electromagnetic radiation that has a shorter wavelength than the light humans can see. It carries more energy than visible light and can sometimes break bonds between atoms and molecules, altering the chemistry of materials exposed to it. UV light can also cause some substances to emit visible light, a phenomenon known as fluorescence. This form of light — which is present in sunlight — can be beneficial to health, as it stimulates the production of vitamin D and can kill harmful microorganisms, but excessive exposure can cause sunburn and increase the risk of skin cancer. UV light has many uses, including disinfection, fluorescent light bulbs, and in astronomy.
The term “ultraviolet” means “beyond violet.” In the visible part of the spectrum, wavelength decreases — and the energy of the electromagnetic waves increases — from red through orange, yellow, green, blue and violet, so UV light has a shorter wavelength, and more energy, than violet light. Wavelengths are measured in nanometers (nm), or billionths of a meter, and ultraviolet wavelengths range between 10nm and 400nm. It can be classified as UV-A, UV-B or UV-C, in order of decreasing wavelength. An alternative classification, used in astronomy, is “near,” “middle,” “far,” and “extreme.”
Disinfection and Sterilization
The effects of UV light on viruses, bacteria, and parasites have led to its use in disinfecting drinking water supplies. It has the advantages of requiring little maintenance, not affecting the taste of treated water, and leaving no potentially harmful chemicals behind. The main disadvantage is that, unlike some chemical methods — such as chlorination — it will not protect against contamination after treatment. UV is also used for sterilization of food and in microbiology laboratories.
Many insects can see ultraviolet light and are attracted to it, so the light is often used in insect traps. These may be used by entomologists to study the insect population in a specific habitat or to trap and kill nuisance insects in restaurants food stores.