Invisible light from the part of the electromagnetic spectrum immediately beyond the violet end of the visible light spectrum. Long wavelength ultraviolet light is termed , intermediate , and short.
Ultraviolet light occurs in sunlight, but much of it is absorbed by the ozone layer. The ultraviolet light (mainly ) that reaches the earth’s surface causes the tanning effects of sunlight and the production of vitamin D in the skin. It can have harmful effects, such as skin cancer (see sunlight, adverse effects of).
Ultraviolet light is sometimes used in phototherapy.
A mercury-vapour lamp (Wood’s light) can also produce ultraviolet light.
This is used to diagnose skin conditions such as tinea because it causes the infected area to fluoresce.
Pupillary constriction in the EYE in response to light. The direct light re?ex involves pupillary constriction in the eye into which a light is shone; the consensual light re?ex is the pupillary constriction that occurs in the other eye. The a?erent or inward pathway of the re?ex is via the optic nerve, and the e?erent or outward pathway is via the occulomotor nerve.... light reflex
n. the sensation experienced, usually after the 36th week of gestation, by many pregnant women, particularly those carrying their first child, as the presenting part of the fetus enters the pelvis. This reduces the pressure on the diaphragm and the woman notices that it is easier to breathe. Compare engagement.... lightening
invisible short-wavelength radiation beyond the violet end of the visible spectrum. Sunlight contains ultraviolet rays, which are responsible for the production of both suntan and – on overexposure – *sunburn. The dust and gases of the earth’s atmosphere absorb most of the ultraviolet radiation in sunlight (see ozone). If this did not happen, the intense ultraviolet radiation from the sun would be lethal to living organisms.... ultraviolet rays
ultraviolet light filtered through a nickel oxide prism, which causes fluorescence in skin and hair affected by some fungal and bacterial infections and is therefore useful in diagnosis. For example, *erythrasma fluoresces coral pink, while scalp ringworm caused by Microsporum species fluoresces green. [R. W. Wood (1868–1955), US physician]... wood’s light
Health Encyclopedia