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

["cvsc1" <cvsc1@xxxxxxxxxxxx>]

Tom et all,
I am still conducting research toward an article. Do you have a reference
that you can list, concerning rod sensitivity to red light maybe with some
specifics toward intensity values.

The books I have on the eye correlate what we have both said, but I have
not found anything specific enough on frequency vs. intensity as it
relates to rods and cones to satisfy my curiosity.
Stan

---------- Original Message ----------------------------------
From: "Tom Harvey" <tbharvey@xxxxxxx>
Reply-To: az-observing@xxxxxxxxxxxxx
Date: Sat, 14 Dec 2002 22:43:29 -0700

>
>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

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