I read in all paper they use UV light with a wave length 254 nm with bacteria and fungi.
My question is why 254 nm exactly?
Regards
254 nm is emitted by low pressure mercury lamps which is the most common UV lamp for disinfection.
Hi Ayat,
Since most germicidal lamps emit at 254 nm, it is considered 'close enough' to 260 nm to achieve the desired antimicrobial effect.
A good summary of this can be found at: http://www.ironbrookuv.com/uv_fundamentals.html
Which states:
MECHANISM OF GERMICIDAL ACTION
The narrow band of UV light lying between the wavelengths of 200 and 300 nm has often been called the germicidal region because UV light in this region is lethal to microorganisms including: bacteria, protozoa, viruses, molds, yeasts, fungi, nematode eggs and algae. The most destructive wavelength is 260 nm which is very close to the wavelength of 254 nm produced by germicidal lamps. UV light's ability to kill the fecal coliform bacteria, Escherichia coil , is directly related to the ability of its genetic material (i.e. nucleic acid) to absorb UV light. UV light causes molecular rearrangements in the genetic material of microorganisms and this prevents them from reproducing. Most microorganisms have relatively short life cycles and therefore depend on rapid reproduction to sustain and grow their population. Therefore, if a microorganism cannot reproduce then it is considered to be dead. Normally when DNA replicates , the Thymine (T) must join the Adenine (A) , and the Cytosine (C) must join with Guanine (G). When DNA is exposed to Ultraviolet Light at a wavelength of 254 nm, an error occurs in the replication process. The Thymine forms a dimer, that is, a double bond between the Thymine molecules. This error prevents the pathogen from reproducing properly and so eventually it dies off.
254 nm is emitted by low pressure mercury lamps which is the most common UV lamp for disinfection.
254 nm the main emition line but other wavelengths also produced by mercury vapors or by luminophores (if present). Finally it filtered with glass depending of glass composition.
A germicidal low pressure lamp should not have any luminophores/fosforesens layer and the material should not be glass but quarts that is transparent down to at least 240 nm.
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