RE's about absorption

SEAN M. HIGGINS HIGGINSS at VAX.CS.HSCSYR.EDU
Tue May 31 13:35:26 EST 1994


One of the evolutionary tales that has been handed down to me
is that chlorophyll, being the most abundant and expensive (in
terms of energy) pigments, evolved to achieve the most bang for
the energy buck (ie a configuration that would best drive the 
light-energy-capture-Rxs with the least input energy).  Hence,
it was explained to me, there must be a reason why chlorophyll
doesn't absorb well in the green spectrum and that reason is
potentially a filtering (or shifting) of green wavelengths by the
earth's atmosphere.  So, are green wavelengths less abundant on
the earth's surface than other wavelengths and might this explain
why human retinas are "...100x more sensitive to green than red..."
(J-CEEESEMAN)?

Which brings me to my next questions...this 100x greater sensitivity
of the human retina for green over red, is this in the cone or rod
system?  It was my understanding that green and red were 
evolutionarily closely related and equally represented in the
retina (at leats in 'normal' color vision) but the rhodopsins had
a comparatively broad absorption spectrum that overlapped the
green spectrum and not the red.  Also, that the rod system comprised
the majority of the retina, was much more sensitive and, as a result,
the activity of the two systems was (rod-night/cone day) was 
almost mutually exclusive.  So, if the 100x greater sensitivity is
in the rod system, might this just be a by-product of night vision
and, in the case of the spotlight filters, might the reds just be
missed in dark theatres?

Sean Higgins
higginss at vax.cs.hscsyr.edu



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