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UltraViolet

 

Ultraviolet, or UV, refers to electro-magnetic radiation with shorter wavelength then visible light, namely in the 400-10nm range. Shorter wavelength means higher frequency, and thus higher energy. Ultraviolet radiation is mainly produced by stars (like our sun), when the hotter the star is, the more UV radiation is produced (due to black body radiation), but there are methods and technology to produce UV radiation in lower temperatures as well.


Due to the high energy carried by UV, it is easily absorbed by most matter. This characteristic is used, amongst other things, to produce fluorescence, and fluorescent lighting. But, at the same time prolonged exposure to UV, especially of the shorter wavelength, can prove harmful to certain types of molecules, especially organic molecules. Thus, UV lamps can be used for sterilization of spaces and equipment in laboratories, medical facilities and food storages.


Some of the UV on the far part of the spectrum (200-10nm) is so easily absorbed, that it can't propagate through the atmosphere at all, and requires vacuum to stay intact. A large portion of the longer wavelength UV is also absorbed by the atmosphere, and almost all radiation with wavelength of 350nm and less is absorbed by glass (which is notoriously transparent for the visible light part of the spectrum). The human eye's cornea and lens are also efficient absorbers of UV.


UV radiation is used in nano-photolithography. By lighting a UV sensitive substrate with UV light, through a mask, which is partially UV absorbent and partially transparent, it's possible to produce a very high resolution pattern. This process is mainly used to produce electronic chips with very high circuit integration.



Many polymers, such as polypropylene, polyethylene and poly(methyl methacrylate) – which make up a large portion of plastic materials used in modern industry, upon absorbing UV radiation, begin a process of chain degradation, and eventually break. A similar problem occurs with pigments and dyes, which tend to change color and fade as a result of prolonged exposure to UV, be it sunlight or fluorescent lighting.


Materials used for absorption of UV, to protect the UV sensitive molecules underneath, are called Ultraviolet Light Absorbers, or UVAs. A challenge lies in designing a UVA so as to minimize the damage from UV radiation to the protected material, make the protection stable and lasting, and also make sure the UVA does not damage the material it's coating by chemical interaction or otherwise.

 

 

 

Across

 

2.   Some UV radiation is so easily absorbed, that it can only travel through _________.

5.   The process of printing using light.

6.   Color material, degrades when exposed to UV radiation.

 

Down

 

1.   Ultraviolet light is a type of electro-magnetic ___________.

3.   An artificial organic molecule type, used a lot in the industry.

4.   A common material, which is transparent to visible light, but absorbs UV almost completely.

 

 

 

 

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