Hi Rick,

thank you for your extensive and interesting contribute.

Your message mentions many times that red light is not good for reading:
"The majority of people can only read with Orangish-Red light when the luminance
is well above the
level which will produce rod saturation."

Perhaps many of LX200 users do not need to read charts - that is the advantage
of the lx200 technology - you simply GOTO! In this case a MUCH weaker red light
is
enough.

What do you think?

Best Regards,

Bostjan


----- Original Message -----
Sent: Wednesday, August 29, 2001 4:25 AM
Subject: [M]: green vs red lighting to preserve night vision


> I had asked Doug Kniffen for some thoughts on the Green vs. Red light since
> he had written the article on then AAAA site. I asked him for permission to
> post his thoughtful reply. (Unfortunately you get to see how long I have
> been out of grad school below.)
>
> Also, I do think experimention in the field is important, but I believe
> discussing this first here saves time. Measure twice (and know the units),
> cut once sort of thing to me.
>
> -----Original Message-----
> Sent: Monday, August 27, 2001 11:10 PM
> Subject: Re: About Light
>
>
> At 01:47 8/27/01 -0400, you wrote:
> >I want to say that I do NOT question your honesty or integrity. I am
> hoping
> >for a clarification. I have studied sensation and perception extensively
> >back in grad school, though I ended up in another field entirely.
> >I was reading your article in the AAAA website. You make a specific
> >statement that I have found in all my studies to be false....
>
> Hi Rick,
>
> Initially this started as experiments in a dome, located in a rural area,
> which facilitated a relatively high degree of dark adaptation. What I
> found was; Using a reading light of a color to which the high resolution
> cones were most sensitive, permitted reading charts at lower luminance (a
> greater degree of dark adaptation) than using light with a color to which
> the low resolution rods were least sensitive.
>
> > In
> >dim light the cones are inhibited from sending information by neurons that
> >check to see if there is sufficient light.
>
> And the signals produced by the rods are ignored if the luminance is
> sufficient to activate the cones. When there is enough light to produce rod
> saturation, the nerves from the eye to the brain have reached maximum
> signal carrying capacity so it isn't possible to acknowledge additional
> response. However the rods themselves are at 98% of maximum sensitivity
> (based upon the amount of rhodopsin available) at saturation luminance.
>
> >This would seem to say that using green light would be a
> >problem. Green is in an optimal response area for rods.
>
> Green (around 550nm) is also optimal for the cones. The rods don't provide
> the spatial resolution needed to read small chart text.
>
> > Under 600nm rods
> >are simply not responsive and by 625nm rhodopsin simply doesn't uncoil its
> >helix.
>
> From what I've read it depends on the luminance. Below the level required
> to produce rod saturation, the rods are more sensitive than the cones.
> Above saturation luminance individual rods do continue to respond to light,
> but since their activity has long been ignored they don't contribute to
> perception at the higher light levels.
>
> >There are twice as many R cones than G cones...
>
> Some time back the visual researchers quit referring the different cone
> types as R,G,B. Now the convention is L,M,S (wavelengths). This was changed
> because of the confusion produced by labeling the Long wavelength cone
> "red" when it was actually most sensitive to "green" (564nm) light.
>
> >If I wanted to optimize my response to light
> >I should be trying for Orangish-Red which has the greatest area of response
> >for R and G cones without any overlap of rods curve.
>
> The key to maximizing night vision is keeping the luminance as low as
> possible. The colors to which the rods respond simply isn't as important as
> staying well below the rod saturation level. The majority of people can
> only read with Orangish-Red light when the luminance is well above the
> level which will produce rod saturation.
>
> >If you have additional information or reading I would be most appreciative.
>
> The single best reference I've seen is "Human Color Vision" (ISBN
> 1-55752-461-0).
>
> >I have learned over the years to question my information and hold nothing
> >sacred.
>
> I agree completely, and question myself much more than others.
>
> A final comment on using green, as opposed to red, for reading star charts;
> After talking about and demonstrating this topic, I've observed that most
> people never really dark adapt to the maximum extent possible. Since the
> only real reason why an artificial light is needed for astronomical
> observing is reading small chart text, and a fairly high percentage of
> people have some degree of presbyopia, green (near the middle of the
> visual spectrum) will permit reading both with lower luminance and
> considerably less eyestrain than using red.
>
> Doug Kniffen
>
>
>

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