Color range of rods?

Discussion in 'Optometry Archives' started by dumbstruck, Oct 25, 2009.

  1. dumbstruck

    dumbstruck Guest

    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.
    dumbstruck, Oct 25, 2009
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  2. dumbstruck

    dumbstruck Guest

    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!
    dumbstruck, Oct 27, 2009
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  3. dumbstruck

    Liz Guest

    Thanks. Looks like a inverted V response from 400nm to a touch above
    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, Oct 29, 2009
  4. 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
    Robert Redelmeier, Oct 29, 2009
  5. dumbstruck

    Liz Guest

    I keep reading that blue light reception is important in night vision,
    than green or red so may trigger neurons easier.
    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.
    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, Oct 29, 2009
  6. 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
    Robert Redelmeier, Oct 30, 2009
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