FreeLists / az-observing / [AZ-Observing] Re: color is not important was Re: How deep can you see?

["Tom Harvey" <tbharvey@xxxxxxx>]

I think the reason that red light is less deleterious to dark adaptation is
that rods are less sensitive to red light than are cones.  Light bleaches
the photosensitive pigments in the rods and cones, the higher the light
input the lower the pigment concentration becomes due to this bleaching (the
chemical change that occurs in bleaching is also the starting point for the
visual response).  Once the pigment is bleached it takes some time to
regenerate, that's why dark adaptation take some minutes.  Now, the lack of
sensitivity of the rods to red light is most likely due to the lack of
absorption of light in that region by the visual pigment in the rods --- no
absorption, no bleaching --- its the absorption of the light that causes the
bleaching reaction.  If you look in a book on vision you can find spectral
sensitivity curves that will show the cones being sensitive to red light at
wavelengths where rod sensitivity has fallen to a very low value.  In short,
if you use red light to read a star chart, your cones are doing the job,
while the rods are not really responding to the red light, so they remain
dark adapted, ready to look again for that faint fuzzy that is supposed to
be in the field of view of your scope.

Tom
----- Original Message -----
From: "cvsc1" <cvsc1@xxxxxxxxxxxx>
To: <az-observing@xxxxxxxxxxxxx>
Sent: Saturday, December 14, 2002 2:36 PM
Subject: [AZ-Observing] color is not important was Re: How deep can you see?


>
> Generalizations from an up-coming article for the SAC web site.
> Taken from lecture notes on Color Theory and the Human Eye.
>
> The eye is comprised of two sets of photo-receptors.
> They are called rods and cones.
> Rods are responsible for illumination intensity.
> Cones are responsible for color.
> The eye is most sensitive to greenish-yellow light, however cones respond
quickest to red light.
>
> Under low light levels, the rods are the primary receptors and the cones
are in effect not functioning.
>
> As illumination is increased the cones start to react and discern color
while the rods begin to protect themselves by bleaching out the pigmentation
within the eye, which is responsible for the increased sensitivity.
>
> Summary:
> If you have enough light intensity to differentiate color your are
degrading your light adapted eye-sight.
> The reason for the red light, is simple your eye adjusts to it's spectrum
quicker, thus improving your adaptation to light.
>
> Color in less important than intensity of light.
>
> Jack put it right when he said
> > I would use dim any color rather than these crimson beacons I see out
there some times.
>
> --
> have a great day, and a clear night
> Stan Clark
> 33.43N, 112.35 W
> Saguaro Astronomy Club
> Webmaster
> www.saguaroastro.org
> --
> --
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>
>


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