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11_ultraviolet.html
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<p class="head">Ultraviolet light</p>
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<p><a class="def">Ultraviolet</a> (UV) <a class="black" href="https://cvertan.github.io/physics4dh.github.io/1_Light.html" target="frameterms">light</a> is one of invisible component of <a class="black" href="https://cvertan.github.io/physics4dh.github.io/13_EM_spectrum.html" target="frameterms">electromagnetic spectrum</a> at the <a class="black" href="https://cvertan.github.io/physics4dh.github.io/15_Wave.html" target="frameterms">wavelengths</a> <a class="def">between 100 nm and 400 nm</a>. UV is just beyond the <a class="black" href="https://cvertan.github.io/physics4dh.github.io/4_Colors%20of%20light.html" target="frameterms">violet</a> end of <a class="black" href="https://cvertan.github.io/physics4dh.github.io/18_visible_light.html" target="frameterms">visible light</a> and has shorter wavelengths and greater <a class="black" href="https://cvertan.github.io/physics4dh.github.io/3_Photon%20energy.html" target="frameterms">energy</a>. </p>
<p>About 10% of the Sun’s <a class="black" href="https://cvertan.github.io/physics4dh.github.io/20_Energy.html" target="_blank">energy</a> output is UV. Only a small part of the Sun’s UV reaches us, since the ozone layer and oxygen within the Earth’s atmosphere effectively blocks most of incoming ultraviolet light. Only some of the UV light of the longer wavelength reaches the Earth’s surface. </p>
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<img src="Figures/UV3.jpg" width="400" height="100">
<div class="desc">Image sources: <a href="https://www.infralia.com/en/uv-light-characteristics/" target="_blank">https://www.infralia.com</a>, <a href="https://marktechopto.com/technical-articles/understanding-ultraviolet-led-applications-and-precautions/" target="_blank">https://marktechopto.com</a> </div>
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<p>UV is classified by wavelength and properties into 3 categories:</p>
<p><b>UV-A</b> (<b>315-400 nm</b>, long <a class="black" href="https://cvertan.github.io/physics4dh.github.io/15_Wave.html" target="frameterms">wave</a> UV, the closest to the visible light) – up to 95% of it can get through the Earth’s atmosphere and reach the Earth’s surface; passes through glass; can cause accelerated ageing of the skin, melanomas and eye diseases (cataracts).</p>
<p><b>UV-B</b> (<b>280-315 nm</b>, harmful) – only up to 5% of it can get through the Earth’s atmosphere and reach the Earth’s surface; doesn’t pass through the ordinary glass but blocked by quartz glass; ensures the production of vitamin D in the organism, responsible for sunburn and producing a tan, can cause some types of cancer. </p>
<p><b>UV-C</b> (<b>200-280 nm</b>, shortest wave UV, most harmful) gets completely trapped in the ozone layer of the atmosphere; doesn’t pass through the ordinary glass but does pass through quartz glass; is detrimental and destroys the DNA and RNA of micro-organisms. UV-C is the only type of UV radiation that is intense enough to combat pathogens, such as bacteria, virus, mold, fungus. For this reason, the UV-C lighting are using for decades in hospitals for sterilization and disinfection. </p>
<p class="acknow">Acknowledgements: [<a class="ref" href=bibliography.html#infralia>infralia</a>], [<a class="ref" href=bibliography.html#sciencelearn>sciencelearn</a>], [<a class="ref" href=bibliography.html#markt>marktechopto</a>].</p>
<p class="important">More on the subject:
<a href="https://www.youtube.com/watch?v=u-97FDd3k48" target="_blank">https://www.youtube.com/1</a>, <a href="https://www.youtube.com/watch?v=-n1oofkvrMc???" target="_blank">https://www.youtube.com/2</a></p>
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