ultraviolet rays


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Related to ultraviolet rays: infrared rays

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.

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.

ultraviolet (UV) rays

Etymology: L, ultra, beyond; OFr, violette + L, radius
electromagnetic radiations found just beyond the violet edge of the visible spectrum, with wavelengths extending to the beginning of x-rays. The wavelengths range from 390 to 290 nm for near-UV rays to 290 to 20 nm for far-UV wavelengths. Ultraviolet radiation in the region of 260 nm can cause photochemical reactions in deoxyribonucleic molecules, causing mutations and destroying microorganisms, including bacteria and viruses.

Ultraviolet rays

Invisible light rays with a wavelength shorter than that of visible light but longer than that of x rays.
Mentioned in: Sunscreens

ultraviolet

denoting electromagnetic radiation of wavelength shorter than that of the violet end of the spectrum, having wavelengths of 4-400 nanometers.

ultraviolet antisepsis
because ultraviolet rays are capable of killing bacteria and other microorganisms, they are sometimes utilized in specially designed cabinets to sterilize objects, and may also be used to sterilize the air in operating rooms and other areas where destruction of bacteria is necessary.
ultraviolet irradiation
the projection of ultraviolet light from a generator is used for the treatment of skin disease and for sterilization of materials.
ultraviolet rays
electromagnetic radiation beyond the violet end of the visible spectrum (at 0.39 to 0.18 μm wavelength) and therefore 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.
Ultraviolet rays can produce sun-burning and affect skin pigmentation. When they strike the skin surface, these rays transform provitamin D, secreted by the glands of the skin, into vitamin D, which is then absorbed into the body.
ultraviolet therapy
the employment of ultraviolet radiation in the treatment of various diseases, particularly those affecting the skin, is used in humans, but not commonly employed in veterinary medicine.

Patient discussion about ultraviolet rays

Q. what does a sun block cream do? and what are a UV rays?

A. It blocks out harmful Ultra violet rays from the skin as the previous entries have related; however it can also block your ability to produce vitamin D. If you live in a northerly area or one that receives limited sunlight, its recommended to get at least 15 minutes of sun a day (this is probably best done with minimal sunblock) and according to personnal sun sensitivity. Another thing to keep in mind is that sunblock works best if applied 20 minutes before sun exposure.

More discussions about ultraviolet rays
References in periodicals archive ?
It's precisely when you can't feel the burn that the sun's ultraviolet rays can cause considerable retinal damage.
The researchers also exposed the cell cultures to ultraviolet rays and measured the amount of DNA damage and the rate of its repair, as well as the percent of surviving melanocytes.
Moreover, if you've had cataract surgery to restore vision, you may be even more vulnerable to the sun's ultraviolet rays.
Any exposure to ultraviolet rays also means that the risk of these damaging the skin in serious ways is increased, and the damage builds up with more exposure (it's 'cumulative').
This chemical gives skin its color and guards against the sun's ultraviolet rays.
Iran's Health Ministry has outlawed the use of tanning beds on health grounds and warned Iranians of the cancer hazards of exposure to ultraviolet rays.
The sun emits ultraviolet rays, an invisible form of radiation that can penetrate the skin and cause skin cancer, which is the most common form of cancer in the United States.
Just as the sun's ultraviolet rays can burn skin, they can also damage epoxy coatings that are unprotected by paint.
Most types of sunglasses are coated with a special material that blocks the sun's ultraviolet rays from hitting a person's eyes.
Concerned that tanning rays can cause skin cancer and eye damage, Ohio Representative Courtney Combs wants to require a doctor's prescription before allowing teens to expose themselves to tanning booths' ultraviolet rays.
Unlike high-altitude ozone, which blocks harmful ultraviolet rays, low-level ozone damages plants, reducing their capacity to take up carbon dioxide.
Sunlight contains ultraviolet rays (UV rays for short).

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