how use ultraviolet light to sterilize?

jayakumar jakku at
Wed Dec 30 10:52:48 EST 1998

Dear members
      In one of the previous mails related to this topic, somebody had
mentioned that UV light only disinfects and does not sterilise.  Let us make
clear the difference between sterilisation and disinfection.  Disinfection.
According to the book "Microbiology" by Pelczar and Krieg, a disinfectant is
an agent that kills the vegetative forms of life while a sterilant destroys
all forms of life, whether it may be vegetative or spores.    UV is actually
a sterilant, since it is very germicidal and hence destroys any
microorganisms which may be directly exposed to it.  But please note, that
since UV does not have much penetrating ability, it is easily stopped or
rather filtered off by any matter which may come between the rays and the
germs.  A UV wavelength of 2650 Angstroms is the best for sterilisation.
The UV rays from sunlight is mostly filtered off by the time it reaches the
earth surface.  The incident light is in the range of 2670 A to 3900 A.  So
sunlight has bactericidal activity albeit to a lesser extent. Other wise we
would all be suffering from serious cases of sunburn and skin cancer.
    UV sterilisation is generally used in labs for sterilising the surfaces
of Laminar flow chambers, and to induce mutation in microorganims under
controlled exposure.
   Moreover UV does not pass through any OPAQUE  material, least of all
plastic.  Water also absorbs UV, as does glass. Quartz is transparent to UV.
   Please comment on this
R. Jayakumar, CSIR-SRF,
School of Biotechnology,
Madurai Kamaraj University,
Madurai - 625021.
tel: +91-452-858464(hostel), 858471(ask for 374 to lab)
fax: +91-452-859105
email: jakku at
-----Original Message-----
From: max at <max at>
To: bionet.microbiology mail newsgroup <bionet-news at>
Date: Tuesday, December 29, 1998 7:52 AM
Subject: Re: how use ultraviolet light to sterilize?

>I find the claim hard to believe. The UV light may pass through the plastic
>or water and kill some bacteria, but I doubt it would be sufficient. I
>like to know if there is some data on this..a research paper etc. I would
>extremely interested.
>In article <mignatz-2712982300290001 at>,
>mignatz at (Dr. Michael J. Miller) wrote:
>>Is there any scientific data to support the claim below?
>>In article <3683ED68.E247049A at>, comfortc at
>>> In Thailand we have easy way to produce bottle drinking water
>>> in the urban area (the province up country). By using UV from sunlight
>>> to disinfect the normal flora in water by bring the bottle of water to
>>> in sunlight for more than 12 hrs. This is the easy way to produce when
>>there are
>>> no sterile expensive equipments.
>>> It can kill the pathogens in water as well.
>>Dr. Michael J. Miller

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