Ultraviolet light or UV is electromagnetic radiation in the wavelength range of 10 to 400 nanometers (nm), which is between x-rays and visible light. Because it is largely invisible to humans, another name for UV is black light. Ultraviolet light that is close to visible light in terms of energy (near ultraviolet UVA and UVB) is non-ionizing radiation. However, energetic (UVC or shortwave) ultraviolet light is ionizing and has an increased capacity to damage DNA and kill cells.
Types of Ultraviolet Light
The discovery of UV light dates back to 1801 when the German physicist Johann Wilhelm Ritter noticed that silver chloride darkened more when exposed to light beyond the range of vision than to violet light. Ritter called this radiation “de-oxidizing rays” to distinguish it from the “heat rays” (infrared radiation) discovered in 1800 at the opposite end of the visible spectrum. The name changed to “chemical rays” and finally “ultraviolet radiation”.
History of UV Light Discovery
Ultraviolet light falls into three categories based on wavelength, according to ISO standard 21348:
- UVA (315-400 nm): Long-wave ultraviolet light, which into the skin and is responsible for skin aging and DNA damage.
- UVB (280-315 nm): Medium-wave ultraviolet light, which can cause sunburns and skin cancer.
- UVC (100-280 nm): Short-wave ultraviolet light, which is mostly absorbed by the Earth’s atmosphere and has germicidal properties.
A similar classification scheme describes UV light based on its proximity to visible light:
- Near ultraviolet or NUV (300-400 nm): NUV is non-ionizing radiation or black light. It is not absorbed by the ozone layer. Insect, birds, fish, and some mammals perceive NUV.
- Middle ultraviolet or NUV (200-300 nm): MUV is mostly absorbed by ozone.
- Far ultraviolet or FUV (122-200 nm): FUV is ionizing radiation that is completely absorbed by ozone.
- Hydrogen Lyman-α (121.6): This is the spectral line of hydrogen.
- Vacuum ultraviolet or VUV (10-200 nm): This is ionizing radiation that is absorbed by oxygen, although 150-200 nm can travel through nitrogen.
- Extreme ultraviolet or EUV (10-121 nm): This is ionizing radiation that is absorbed by the atmosphere.
Sources of Ultraviolet Radiation
The primary source of UV light is the Sun, which emits radiation across the entire UV spectrum. However, only UVA and UVB radiation reach the Earth’s surface, as the ozone layer absorbs UVC. Other sources of UV light include artificial sources like black lights, tanning lamps, mercury vapor lamps, high pressure xenon lamps, welding arcs, and germicidal lamps.
Ultraviolet Light and the Ozone Layer
The ozone layer is a crucial component of Earth’s stratosphere that absorbs most of the Sun’s UVC radiation and a portion of UVB radiation. Chlorofluorocarbons (CFCs) have contributed to the depletion of the ozone layer, increasing the levels of UV radiation reaching the Earth’s surface and posing risks to human health and the environment.
Effects of Ultraviolet Radiation on the Human Body
Excessive exposure to UV radiation has adverse effects on the human body. Ultraviolet radiation damages collagen, destroys vitamin A in the skin, harms the eyes, and causes DNA damage. UVB overexposure produces a sunburn, which is a visible sign of skin damage. Chronic exposure to UV radiation, including both UVA and UVB, is associated with premature skin aging and an increased risk of skin cancer. Melanoma, the most dangerous form of skin cancer, has been strongly linked to intermittent, intense exposure to UV radiation.
While too much ultraviolet light is harmful, the World Health Organization advises that some exposure is beneficial. UVB causes vitamin D production in the body. One effect of vitamin D is that it promotes serotonin production, a neurotransmitter that causes a sense of well-being. UV light treats certain skin conditions, such as eczema, psoriasis, scleroderma, and atopic dermatitis. Ultraviolet light also plays a role in regulating circadian rhythms and immune function.
Animals and Ultraviolet Light Perception
Several animals can perceive UV light, including insects, birds, and some mammals. Bees and butterflies use UV vision to locate flowers, while birds use it for navigation and mate selection. Some rodents, such as mice and rats, also have UV sensitivity.
Can Humans See UV Light?
Most people cannot perceive UV light under normal conditions, although children and young adults often perceive “violet” as ending around 315 nm (into the UVA range). Older adults typically see only as far as 380 or 400 nm. The lens of the human eye blocks most ultraviolet radiation even though the retina can detect it. Some people who are missing a lens (aphakia) or who have an artificial lens (as from cataract surgery) report seeing ultraviolet light. Humans lack the color receptor for ultraviolet, so the light appears as a violet-white to blue-white color.
Uses of Ultraviolet Light
Ultraviolet light has numerous practical applications across various industries and fields. Some of the most prominent uses include:
- Disinfection and Sterilization: UVC radiation is highly effective in destroying bacteria, viruses, and other microorganisms, making it an invaluable tool for disinfecting water, air, and surfaces in hospitals, laboratories, and public spaces.
- Odor removal: UVC breaks apart large molecules responsible for odors and is part of some air purification systems.
- Tanning: UVA and UVB radiation are used in artificial tanning devices to stimulate melanin production and create a tanned appearance. However, excessive use of tanning beds increases the risk of skin cancer.
- Phototherapy: UV light, especially narrowband UVB, is used in medical phototherapy to treat skin conditions such as psoriasis, eczema, and vitiligo.
- Forensics: Forensic investigators use ultraviolet light to detect bodily fluids, counterfeit currency, and forged documents.
- Fluorescence and Material Analysis: UV light induces fluorescence in certain materials, which can then be observed and analyzed. This technique has applications in molecular biology, mineralogy, art conservation, and chemistry.
- Insect Traps: UV light attracts many insects, making it useful for creating insect traps and monitoring insect populations for ecological studies.
- Photocatalysis: UV light initiates photocatalytic reactions, leading to the breakdown of organic pollutants in water and air for environmental remediation.
- Bolton, James; Colton, Christine (2008). The Ultraviolet Disinfection Handbook. American Water Works Association. ISBN 978-1-58321-584-5.
- Haigh, Joanna D. (2007). “The Sun and the Earth’s Climate: Absorption of solar spectral radiation by the atmosphere”. Living Reviews in Solar Physics. 4 (2): 2. doi:10.12942/lrsp-2007-2
- Hockberger, Philip E. (2002). “A History of Ultraviolet Photobiology for Humans, Animals and Microorganisms”. Photochemistry and Photobiology. 76 (6): 561–569. doi:10.1562/0031-8655(2002)0760561AHOUPF2.0.CO2
- Hunt, D. M.; Carvalho, L. S.; Cowing, J. A.; Davies, W. L. (2009). “Evolution and spectral tuning of visual pigments in birds and mammals”. Philosophical Transactions of the Royal Society B: Biological Sciences. 364 (1531): 2941–2955. doi:10.1098/rstb.2009.0044
- Young, S.N. (2007). “How to increase serotonin in the human brain without drugs”. Journal of Psychiatry and Neuroscience. 32 (6): 394–399.