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| Science Forum Index » Medicine - Vision Forum » Color range of rods?... |
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| dumbstruck... |
 Posted: Sun Oct 25, 2009 10:19 am |
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Rods are said to detect white or greys, but that is simply the
perception and don't they really detect aqua? I seem to remember they
are optimized for 558nm, and mostly exclude red. But what is the shape
of their response graph (non spikey?), or what is the breadth of
wavelengths where response is significant.
Partly I am wondering why so many find a bright blue/green so
pleasing. At first I thought maybe because the rods are stimulated the
most there, but they are probably shut down in brightness. Maybe it is
because there is a relative dead spot in the cone response graph in
the high 400s nm which is rarely stimulated except with tropical
shores for example. |
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| Salmon Egg... |
| Posted: Sun Oct 25, 2009 5:14 pm |
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In article
<292e54a2-43a9-4745-ac27-e7d3e53219d0 at (no spam) 12g2000pri.googlegroups.com>,
dumbstruck <dumbstruc at (no spam) gmail.com> wrote:
[quote]Rods are said to detect white or greys, but that is simply the
perception and don't they really detect aqua? I seem to remember they
are optimized for 558nm, and mostly exclude red. But what is the shape
of their response graph (non spikey?), or what is the breadth of
wavelengths where response is significant.
Partly I am wondering why so many find a bright blue/green so
pleasing. At first I thought maybe because the rods are stimulated the
most there, but they are probably shut down in brightness. Maybe it is
because there is a relative dead spot in the cone response graph in
the high 400s nm which is rarely stimulated except with tropical
shores for example.
[/quote]
look up scotopic vision. I remember a curve being published in the RCA
Electrooptical Handbook. It probably is in the OSA Handbook and many
other places.
Bill
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As the years go by, dying just before having to fill out a tax return has merit. |
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| dumbstruck... |
| Posted: Tue Oct 27, 2009 10:00 am |
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Guest
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On Oct 25, 1:14 pm, Salmon Egg <Salmon... at (no spam) sbcglobal.net> wrote:
[quote] dumbstruck <dumbst... at (no spam) gmail.com> wrote:
Rods are said to detect white or greys, but that is simply the
perception and don't they really detect aqua? I seem to remember they
are optimized for 558nm, and mostly exclude red. But what is the shape
of their response graph (non spikey?), or what is the breadth of
wavelengths where response is significant.
look up scotopic vision. I remember a curve being published in the RCA
Electrooptical Handbook. It probably is in the OSA Handbook and many
other places.
[/quote]
Thanks. Looks like a inverted V response from 400nm to a touch above
600, with 500+ the peak. So we DO see in shades of aqua at night! |
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| Mike Tyner... |
| Posted: Tue Oct 27, 2009 7:41 pm |
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"dumbstruck" <dumbstruc at (no spam) gmail.com> wrote
[quote]Thanks. Looks like a inverted V response from 400nm to a touch above
600, with 500+ the peak. So we DO see in shades of aqua at night!
[/quote]
We can see aqua light with the rod system, of course. We aren't blind to it.
We just perceive it as gray. We have no way of distinguishing it from other
colors, unless cones are stimulated.
-MT |
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| Liz... |
| Posted: Wed Oct 28, 2009 8:07 pm |
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[quote]Thanks. Looks like a inverted V response from 400nm to a touch above
600, with 500+ the peak. So we DO see in shades of aqua at night!
We can see aqua light with the rod system, of course. We aren't blind to it.
We just perceive it as gray. We have no way of distinguishing it from other
colors, unless cones are stimulated.
[/quote]
Other mammals that see at night have blue and green cones, but AFAIK
they are seeing at night with their rods - they're not seeing in aqua,
I don't think.
I keep reading that blue light reception is important in night vision,
so maybe the blue cones are the last ones to see color before
everything gets so dark that only rods are involved. ? That, or
blue light is the last wavelength to disappear when it gets dark?
Liz
Indianapolis |
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| Robert Redelmeier... |
| Posted: Thu Oct 29, 2009 2:13 am |
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Liz <fraternobombus at (no spam) yahoo.com> wrote in part:
[quote]Thanks. Looks like a inverted V response from 400nm to a touch above
600, with 500+ the peak. So we DO see in shades of aqua at night!
We can see aqua light with the rod system, of course. We aren't blind to it.
We just perceive it as gray. We have no way of distinguishing it from other
colors, unless cones are stimulated.
Other mammals that see at night have blue and green cones, but AFAIK
they are seeing at night with their rods - they're not seeing in aqua,
I don't think.
I keep reading that blue light reception is important in night vision,
so maybe the blue cones are the last ones to see color before
everything gets so dark that only rods are involved. ? That, or
blue light is the last wavelength to disappear when it gets dark?
[/quote]
Could easily be. Blue wavelengths of light have more energy
than green or red so may trigger neurons easier.
OTOH, IIRC humans are most sensitive to green light (see best
by green at low light levels).
-- Robert |
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| Salmon Egg... |
| Posted: Thu Oct 29, 2009 7:16 am |
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Guest
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In article
<91764ccb-7744-42a2-a2dc-6dc5babfb741 at (no spam) p8g2000yqb.googlegroups.com>,
Liz <fraternobombus at (no spam) yahoo.com> wrote:
[quote]Thanks. Looks like a inverted V response from 400nm to a touch above
600, with 500+ the peak. So we DO see in shades of aqua at night!
We can see aqua light with the rod system, of course. We aren't blind to it.
We just perceive it as gray. We have no way of distinguishing it from other
colors, unless cones are stimulated.
Other mammals that see at night have blue and green cones, but AFAIK
they are seeing at night with their rods - they're not seeing in aqua,
I don't think.
I keep reading that blue light reception is important in night vision,
so maybe the blue cones are the last ones to see color before
everything gets so dark that only rods are involved. ? That, or
blue light is the last wavelength to disappear when it gets dark?
Liz
Indianapolis
[/quote]
The cones are "designed" (selected for evolutionist and literally
designed for creationists) to provide color cues to the brain. That is
why there are three different kinds of cones, each kind having its own
color pigment. With only one kind of rod, no color information can be
extracted.
I can only speculate as to why there may be no red sensitivity in some
dark adapted animals. The photon energy is least for long wavelengths.
That means that thermal excitation will energize red absdorbing dyes or
pigments more readily than those that require more energetic photons for
green and blue. In radar terms, red receptors will have a higher false
alarm rate.
Bill
--
As the years go by, dying just before having to fill out a tax return has merit. |
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| Liz... |
| Posted: Thu Oct 29, 2009 10:33 am |
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[quote]I keep reading that blue light reception is important in night vision,
so maybe the blue cones are the last ones to see color before
everything gets so dark that only rods are involved. ? That, or
blue light is the last wavelength to disappear when it gets dark?
Could easily be. Blue wavelengths of light have more energy
than green or red so may trigger neurons easier.[/quote]
[quote]OTOH, IIRC humans are most sensitive to green light (see best
by green at low light levels).[/quote]
I don't know. This is confusing. I'm not sure what causes us to be
using mainly our blue cones in dim light.
[quote]Other mammals that see at night have blue and green cones, but AFAIK
they are seeing at night with their rods - they're not seeing in aqua,
I don't think.
I can only speculate as to why there may be no red sensitivity in some
dark adapted animals.
[/quote]
I believe the theory is that mammals LOST our red and UV cones. We
screwed up.
I think (??) that most vertebrates have FOUR cones - red, green, blue,
and UV. They had these back eons ago.
Those that remained diurnal, like dinosaurs (now birds), and fish
(still fish today), and I think some reptiles (now lizards) have
retained 4-cone vision.
Mammals became noctural, to such an extent that they didn't need all
those cones, they needed rods, and so one or two of the cones
disappeared. Dinosaurs had all the good diurnal niches. After
dinosaurs vanished, some mammals came back into the light.
When primates became diurnal again, one of our cones mutated to give
us a third (red) cone, and we regained 3-cone vision. We never re-
acquired the UV cone. Fellow mammals who stayed nocturnal (like deer)
stuck with just 2 cones.
I do not know if deer see UV.
Thus, humans now have night vision that is much worse than that of
most mammals, and day vision that is better than that of most mammals
but worse than that of birds.
At least, this is roughly my understanding of it all. There may be
several errors in there.
Liz |
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| Robert Redelmeier... |
| Posted: Fri Oct 30, 2009 3:43 am |
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Liz <fraternobombus at (no spam) yahoo.com> wrote in part:
[quote]I don't know. This is confusing. I'm not sure what causes
us to be using mainly our blue cones in dim light.
[/quote]
Possibly because as light levels (number of photons) are reduced,
blue cones are the last to stop firing if they require a threshold
energy to fire. A blue photon has twice the energy of a red photon.
-- Robert |
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| Salmon Egg... |
| Posted: Fri Oct 30, 2009 8:13 am |
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Guest
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In article <hceqit$6le$1 at (no spam) aioe.org>,
Robert Redelmeier <redelm at (no spam) ev1.net.invalid> wrote:
[quote]Liz <fraternobombus at (no spam) yahoo.com> wrote in part:
I don't know. This is confusing. I'm not sure what causes
us to be using mainly our blue cones in dim light.
Possibly because as light levels (number of photons) are reduced,
blue cones are the last to stop firing if they require a threshold
energy to fire. A blue photon has twice the energy of a red photon.
-- Robert
[/quote]
It is not so much that red absorbing cell firing threshold is greater
than for other visual pigments. Lower energy photons will fire the red
sensitive cones. as multiple The thermal jostling of particles such as
molecules and electrons can excite the red absorbing pigment in the
ABSENCE of light. To prevent getting false alarms this way, various
neural circuits inhibit the generation of nerve impulses unless there
are multiple photon absorptions within a short interval of time.
Analogous electronic circuits are called coincidence circuits. I have no
personal knowledge of the specific way neurons implement such functions.
Green and blue receptors take higher photon energy to be excited
compared to red and are intrinsically less likely to be thermally
excited. Thus, they do not need the same protection against false alarms.
Bill
--
As the years go by, dying just before having to fill out a tax return has merit. |
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