ultraviolet radiation


August 15, 2022

Ultraviolet radiation or UV radiation is called electromagnetic radiation whose wavelength is approximately between 100 nm (100×10−9 m) and 400 nm (400×10−9 m). Its name comes from the fact that its range starts from wavelengths shorter than what the human eye identifies as violet light, but said light or wavelength is invisible to the human eye as it is above the visible spectrum. This radiation is an integral part of the sun's rays and produces several effects on health as it is a radiation between non-ionizing and ionizing.[1]


The discovery of ultraviolet radiation is associated with the experimentation of the darkening of silver salts when exposed to sunlight. In 1801 the German physicist Johann Wilhelm Ritter discovered that invisible rays just beyond the violet end of the visible spectrum were especially effective at darkening paper impregnated with silver chloride. He called these rays "deoxidizing rays" to emphasize their chemical reactivity and to distinguish them from "heat rays" (discovered by William Herschel) which were on the other side of the visible spectrum. Shortly thereafter the term "chemical rays" was adopted. These two terms remained quite popular throughout the 19th century. Finally these terms were giving way to the most modern ones of infrared and ultraviolet radiation respectively.[2]


Ultraviolet rays are invisible to most humans. The lens of the human eye blocks most of the radiation in the 300-400nm (nanometer) wavelength range; shorter wavelengths are blocked by the cornea.[3] Humans also lack color receptor adaptations for ultraviolet rays. However, photoreceptors in the retina are sensitive to near ultraviolet rays, and people who lack a lens (a condition known as aphakia) perceive near ultraviolet rays as whitish-blue or whitish-violet.[4] Under some conditions, children and young adults can see ultraviolet down to wavelengths around 310 nm.[5][6] Near-ultraviolet radiation is visible to insects, some mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays; this gives birds "true" UV vision.[7][8]


According to their wavelength, several subtypes of ultraviolet rays are distinguished:[9] Various solid-state and vacuum devices have been explored for use in different parts of the UV spectrum. Many approaches try to adapt sensing devices to visible light, but these can suffer from unwanted response to visible light and various instabilities. Ultraviolet can be detected by suitable photodiodes and photocathodes, which can be adapted to be sensitive to different parts of the UV spectrum. There are photomultipliers sensitive to UV rays. Spectrometers and radiometers are manufactured to measure UV radiation. Silicon detectors are used across the spectrum.[10] Vacuum ultraviolet, or VUV, wavelengths (below 200nm) are strongly absorbed by molecular oxygen in the air, although longer wavelengths, around 150-200nm, can propagate through nitrogen . Therefore, scientific instruments can use this spectral range operating in an oxygen-free atmosphere (commonly pure nitrogen), without the need for expensive vacuum chambers. Some significant examples are 193 nm photolithography equipment, for the manufacture of integrated circuits, and circular dichroism spectrometers. The technology for VUV instrumentation was driven largely