Ultraviolet light, also known as UV light, is a type of electromagnetic radiation that exists beyond the visible light spectrum’s violet end. It has a shorter wavelength than visible light and thus carries more energy. Although UV radiation is a component of sunlight, much of it is filtered out by the ozone layer on the Earth’s surface, leaving only a small portion to reach the surface. UV light causes tanning and stimulates vitamin D production; however, the higher energy levels in UV light can cause cell damage. Although UV irradiation can be used to kill harmful microorganisms, it can also cause sunburn and eye problems in humans, as well as increase the risk of skin cancer.
UV light is divided into three types based on wavelength, with type A having the longest wavelength and type C having the shortest. Although the Earth is exposed to all three types of UV radiation, shorter wavelengths are absorbed more efficiently by the atmosphere, resulting in more UVA reaching the surface than UVB and all UVC being absorbed, with the exception of very high altitudes. UVB emits more energy because of its shorter wavelengths. This energetic form of UV light can cause chemical changes in materials exposed to UV irradiation by breaking the bonds that hold molecules together.
UV radiation can have both beneficial and harmful effects. Vitamin D3 is produced in response to ultraviolet light, which is necessary for human health. Lack of exposure to sunlight can cause a deficiency, which can have negative health consequences.
When the skin is exposed to UVB, vitamin D3 is naturally produced from a precursor compound found in the skin. UV irradiation of a compound found in plants can produce another form of vitamin D2, known as D2. This vitamin supplement has similar effects to D3 and is available as a supplement.
Although some UVB is required to bring the melanin to the surface, UVA stimulates the production of the pigment melanin in the skin, resulting in tanning. UV lamps designed to produce primarily UVA are used in tanning beds to promote tanning while reducing the risk of burning and skin cancer. However, evidence suggests that UVA may play a role in skin cancer and that people who use tanning beds frequently have a higher risk of developing the disease. UVB is more harmful, but UVA penetrates deeper into the skin due to its longer wavelength. Both types contribute to skin aging, and too much exposure can lead to cataracts in the eyes.
There is concern that as ozone levels in the upper atmosphere decline, more UVB will reach the surface, causing damage to living organisms. Both terrestrial and aquatic life may be harmed. UV can affect phytoplankton, the simple marine photosynthesizing organisms that make up the first level of the marine food chain, down to a depth of 66 feet (20 meters).
The World Health Organization has published guidelines for reporting UV levels in response to specific concerns about the effects of UV radiation on human health. A UV index is used in many areas to inform the public about the likely level of UV radiation for the following day. The Environmental Protection Agency (EPA) in the United States has developed a UV index ranging from 1 to 15 to indicate the risk of skin damage. A value of 2 or less is considered low, while a value of 11 or more is considered extreme.
UV’s effect on DNA, which absorbs UVB wavelengths, causes the majority of damage to organisms. UV irradiation can prevent cells from reproducing, despite the fact that repair mechanisms have evolved to restore damaged DNA. UV irradiation can also cause cancer by causing cell death or abnormal growth.
UV irradiation’s harmful effects can be put to good use in killing or deactivating pathogenic microorganisms. Microorganisms are particularly vulnerable to UV light damage because they are made up of single cells with little or no radiation protection. When pathogenic viruses and bacteria are exposed to sunlight, they usually do not survive for long. A UV germicide that emits more UV radiation than sunlight can be used to disinfect hospitals and sterilize water.