Re: visible light damage to DNA

[William Prestwich <prestwic@mcmail.cis.McMaster.CA>]

I find it surprising that significant effects occur in the visible
region. As someone remarked an indirect effect in which an excited
chromophore creates singlet oxygen would be the most likely effect.
This is the basis of photodynamic therapy. However in that treatment
a porphyrin (if I remember) is introduced at as high a concentration 
as possible, and combined with the light field produced by a laser,
which of course results in an enormous fluence. For naturally occurring
radiation fields and normal levels of endogenous chromophores the
interaction rate would be very small indeed. When one takes into
consideration the natural repair mechanisms, it is very surprising, to me
at any rate, that there would be any obsevable effect.

If however, visible light is indeed carcinogenic, then to be consistent
shouldn't the Green party and like minded folk be campaigning to
shut down all sources of visible light?
Cheers,
Bill Prestwich,
McMaster University,
Hamilton, Ont.
E-mail:prestwic@mcmaster.ca 



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