ultraviolet

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ultraviolet

 [ul″trah-vi´o-let]
denoting electromagnetic radiation of wavelength shorter than that of the violet end of the spectrum, having wavelengths of 4–400 nanometers.
ultraviolet A (UVA) ultraviolet radiation with wavelengths between 320 and 400 nm, comprising over 99 per cent of such radiation that reaches the surface of the earth. Ultraviolet A enhances the harmful effects of ultraviolet B radiation and is also responsible for some photosensitivity reactions; it is used therapeutically in the treatment of a variety of skin disorders.
ultraviolet B (UVB) ultraviolet radiation with wavelengths between 290 and 320 nm, comprising less than 1 per cent of the ultraviolet radiation that reaches the earth's surface. Ultraviolet B causes sunburn and a number of damaging photochemical changes within cells, including damage to DNA, leading to premature aging of the skin, premalignant and malignant changes, and a variety of photosensitivity reactions; it is also used therapeutically for treatment of skin disorders.
ultraviolet C (UVC) ultraviolet radiation with wavelengths between 200 and 290 nm; all of this type of radiation is filtered out by the ozone layer so that none reaches the earth's surface. Ultraviolet C is germicidal and is also used in ultraviolet phototherapy.
ultraviolet rays electromagnetic radiation beyond the violet end of the visible spectrum; they are not visible to humans. They are produced by the sun but are absorbed to a large extent by particles of dust and smoke in the earth's atmosphere. They are also produced by the so-called sun lamps. They can produce sunburn and affect skin pigmentation, causing tanning. When they strike the skin surface they transform provitamin D, secreted by the glands of the skin, into vitamin D, which is then absorbed into the body. Because ultraviolet rays are capable of killing bacteria and other microorganisms, they are sometimes used to sterilize objects in specially designed cabinets, or to sterilize the air in operating rooms and other areas where destruction of bacteria is necessary.
ultraviolet therapy the employment of ultraviolet radiation in the treatment of diseases, particularly those affecting the skin. See also PUVA therapy and photochemotherapy. Among the diseases that respond to this form of therapy are acne vulgaris, psoriasis, and external ulcers.

Dosage. The dosage unit of ultraviolet radiation is expressed as minimal erythema dose (MED). Because of varying degrees of skin thickness and pigmentation, human skin varies widely in its sensitivity to ultraviolet radiation. The MED refers to the amount of radiation that will produce, within a few hours, minimal erythema (redness caused by engorgement of capillaries) in the average Caucasian skin. Dosage for individual patients is prescribed according to probable sensitivity as determined by that individual's skin type as compared to average sensitivity.
Degrees of Erythema. Minimal erythema is a first degree erythema and usually is produced after about 15 seconds of exposure to a high-pressure mercury arc in a quartz burner placed at a distance of 75 cm (30 in) from the skin. A second degree erythema results from a dose of about 2.5 MED; its effects become apparent about 4 to 6 hours after application and are followed by slight peeling of the skin. A third degree erythema is produced by about 5 MED; it may become apparent within 2 hours after application and is accompanied by edema followed by marked desquamation. A fourth degree erythema is produced by about 10 MED and is characterized by blistering.
Precautions. Ultraviolet therapy is safe only in the hands of a skilled and knowledgeable therapist. Areas of “thin skin” that may be burned more readily than that receiving treatment must be protected by wet towels or dressings. The eye is highly sensitive to ultraviolet radiation; therefore some form of protection, such as goggles, compresses, or cotton balls, should be provided for both the patient and the therapist to avoid damage to the conjunctiva and cornea.



Certain drugs, such as the sulfonamides, greatly increase sensitivity to ultraviolet radiation. All patients scheduled for this form of therapy should be questioned in regard to the medication they are taking so the dosage can be adjusted accordingly or the treatment deferred.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

ul·tra·vi·o·let (UV, uv),

(ŭl'tră-vī'ō-let),
Denoting electromagnetic rays at higher frequency than the violet end of the visible spectrum.
Farlex Partner Medical Dictionary © Farlex 2012

ul·tra·vi·o·let

(ŭl'tră-vī'ŏ-lĕt)
Denoting electromagnetic rays at higher frequency than the violet end of the visible spectrum.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

ultraviolet (UV) 

Radiant energy of wavelengths smaller than those of the violet end of the visible spectrum and longer than about 1 nm. The wave band comprising radiations between 315 and 380 nm is referred to as UV-A. Excessive exposure to these radiations can cause cataract. The wave band comprising radiations between 280 and 315 nm is referred to as UV-B. Excessive exposure to all these radiations can cause photokeratitis and corneal opacity, while radiations between 295 and 315 nm can cause cataract. The wave band comprising radiations between 200 and 280 nm is referred to as UV-C. Excessive exposure to these radiations can cause photokeratitis and corneal opacity. See blepharospasm; actinic keratoconjunctivitis; excimer laser; absorptive lens; nanometre; pinguecula; wavelength.
Table U1 Divisions of the ultraviolet spectrum
UV-A (near)380-315 nm
UV-B (middle)315-280 nm
UV-C (far)280-200 nm
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann
References in periodicals archive ?
UVA radiation is known to cause extensive protein modification [39].
Douki, "Cyclobutane pyrimidine dimers are predominant DNA lesions in whole human skin exposed to UVA radiation," Proceedings of the National Academy of Sciences of the United States of America, vol.
The current panel of 34 sunscreens tested contains ingredients that protect against UVA radiation, which were lacking from products tested in previous studies (14, 16).
The second study, published by the same authors in the journal Molecular Carcinogenesis, shows that instead of beneficially killing cells damaged by UVA radiation, treatment with silibinin protects human skin cells from damage by UVB radiation, which makes up about five percent of the sun's radiation reaching Earth.
Two sets of experiments were performed: the first one involves the correlation between reaction time and accumulated dose of UVA, and the other relates the reaction directly to the dose of UVA radiation. In the first set of experiments, aliquots of 30 mL were collected at intervals of 20 min up to 60 min of reaction and at very 30 min above 60 min of reaction up to 150 min.
A meteorological station was established at the Dead Sea basin (Neve Zohar) to continuously monitor solar global, UVB and UVA radiation, measure spectral selectivity within the ultraviolet spectrum and investigate other relevant bio-climatological parameters.
Data confirm that the strawberry extract, especially at a concentration of 0.5 mg/ml, displays photoprotective properties in those fibroblasts exposed to UVA radiation, it increases cell survival and viability and decreases damage in the DNA when compared with control cells.
After the supplementation period, the subjects were exposed to two MEDs of UVB and UVA radiation. Skin biopsies taken from the volunteers were analyzed to determine the number of sunburn cells formed after the exposure to radiation.
If you take babies to the beach keep them in a pram and use a "baby sun protective cover" with a UPF (ultraviolet protection factor) rating; Use sunscreens products protecting against both UVB and UVA radiation; Apply sunscreen products regularly, and in sufficient quantity, to maintain the protection claimed.
"Now we know that UVA radiation causes cancer too," says Dr.
The measurements of UVA radiation intensity were carried out by a radiometer UVA-356 HA, the sensor of which registers UV radiation within spectral response 320-400 nm (Figs.