Ultraviolet

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Ultraviolet 


P.K.Ghatak, MD

No 71.



 Human eyes are unable to see Ultraviolet (UV), but insects, birds and dogs are capable of seeking objects in UV. Ultraviolet light is longer than X-ray in their wavelength but shorter than the violet light on the Electromagnetic spectrum. Flowers display petals in UV light for bees and other insects to visit, offering nectar and in the process, insects pollinate flowers.

A German scientist Johann Ritter was experimenting with light waves beyond the visible parts of the light. He used Silver Chloride painted papers to detect the presence of light waves and in 1801, he detected UV light.

The Earth receives UV light mostly from the sun and also from Jupiter, stars, other planets of the solar system, aurora, and white dwarf. Ozone layer in the upper atmosphere blocks UV light, concentration of ozone varies based on location and presence of Ozone destroying substances made by humans. 


Hummingbirds have a special retinal receptor for visualizing colors - green and red in UV light.


Man made UV light is used in industries and medical sciences.

UV light is subdivided into 3 categories - UV-A, UV-B and UV-C.


UV-A. The wavelength of UV-A is between 315 to 400 nm (nanometers). It is absorbed by the atmosphere.

UV-B. It has a wavelength between 200 to 300 nm. It is harmful, it produces sunburn and DNA damages. Ozone layer absorbs UV-B and is most noticeable over the Antarctic and South America. Human made gases in the atmosphere can thin the Ozone layer.

UV-C. It has a wavelength between 100 to 280 nm. It is completely absorbed by the atmosphere. UV light is non -ionizing.


Man Made UV:

UV is generated from gasses and from solid materials

 When electric current or laser light is applied to Mercury vapor in an enclosed vacuum tube, the UV light is generated. By using filters, a specific all subvarieties of UV light are produced.  Other gases like Xenon, Hydrogen isotope Deuterium, Argon and Xenon also generate UV light.

LED light is UV light. A semiconductor, aluminum -gallium Nitrite generates UV light when electric current is applied and the vacuum of the light bulbs are not required. The element is painted with phosphorus to produce visible light.


Use of UV:

UV is used in medical fields, both for diagnosis of fungal diseases. UV light used in tanning salons, in the treatment of Psoriasis, eczema, vitiligo, T- Cell lymphoma, and Jaundice in newly born babies.

UV rays produce Vitamin D in the skin on exposure to sunlight.


Adverse effects of UV light on humans.

Basal cell carcinoma, malignant melanoma and damages to DNA.


There is extensive use of UV in industries. UV light speeds up curing of ink, paint, adhesive, circuit board.   UV-C light is used in sterilization of surfaces, air and water bodies.

Sunglasses and Camera lenses are coated with agents that completely absorb UV light.


Special protective function of Skin and Eyes:

Hair on the skin contains Keratin, it absorbs UV light and prevents damage to skin. Likewise, cornea absorb UV light and inner structures of eyes are protected.


Special case of Polar bears.

Polar bears are exposed to 24 hour days in summer months with a large amount of UV but show no ill effects because underneath the fur, the bears have dark black skin. It completely absorbs UV light. Polar bears also have a third Eyelid which is impervious to UV light.


Use of UV in Astrophysics.

Astronomers position their space telescopes above the Earth atmosphere to eliminate any interference from it. One exciting study is to observe the birth of a star.


Common UV gadgets:

Wood’s light. This runs on a 6- or 10-volt battery, used in the diagnosis of fungal skin infection.

Mercury vapor Lamp.  Used in industries.

Excimer lamp. In this type of lamps, no mercury is used, instead Xenon or other noble gases are used.


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