Color range of rods?

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.

On Oct 25, 1:14*pm, Salmon Egg <Salmon...@sbcglobal.net> wrote:
> *dumbstruck <dumbst...@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.

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!

> > 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

Liz <(E-Mail Removed)> wrote in part:
>> > 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?

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

> 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.

>OTOH, IIRC humans are most sensitive to green light (see best
by green at low light levels).

I don't know. This is confusing. I'm not sure what causes us to be
using mainly our blue cones in dim light.

> > 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.

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

Liz <(E-Mail Removed)> 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