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.

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

/ul·tra·vi·o·let/ (UV) (ul″trah-vi´o-let) denoting electromagnetic radiation between violet light and x-rays, having wavelengths of 200 to 400 nanometers. UVA is that from 320 to 400 nm, UVB is that from 290 to 320 nm, and UVC is that from 200 to 290 nm.
ultraviolet A  (UVA) ultraviolet radiation with wavelengths between 320 and 400 nm, comprising over 99 per cent of that reaching the surface of the earth. It enhances the harmful effects of UVB, is responsible for some photosensitivity reactions, and is used therapeutically in the treatment of various skin disorders.
ultraviolet B  (UVB) ultraviolet radiation with wavelengths between 290 and 320 nm, comprising 1 per cent of that reaching the surface of the earth. It 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 various photosensitivity reactions; it is also used therapeutically in the treatment of skin disorders.
ultraviolet C  (UVC) ultraviolet radiation with wavelengths between 200 and 290 nm, all of which is filtered out by the ozone layer and does not reach the surface of the earth; it is germicidal and is also used in ultraviolet phototherapy.

ultraviolet (UV)

[-vī′ələt]
Etymology: L, ultra + Fr, violette
light beyond the range of human vision, at the short end of the spectrum, or that part of the electromagnetic spectrum with wavelengths between about 10 and 400 nm. Equivalently, an ultraviolet photon has an energy between 5 and 500 eV. It occurs naturally in sunlight. It burns and tans the skin and converts precursors in the skin to vitamin D. Ultraviolet lamps are used in the control of infectious airborne bacteria and viruses and in the treatment of psoriasis and other skin conditions. Black light is ultraviolet light used in fluoroscopy. See also angstrom, light, radiation, spectrum.

ul·tra·vi·o·let

(ŭl'tră-vī'ŏ-lĕt)
Denoting electromagnetic rays at higher frequency than the violet end of the visible spectrum.

ultraviolet (UV),

n electromagnetic radiation that has shorter wavelengths than visible light; used in chemical analytical techniques and antisepsis.

ultraviolet (UV) spectroscopy,

n method used to measure the absorption of ultraviolet light (UV) in wavelength units to identify substances within a mixture. See also ultraviolet (UV).

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

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.
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