Scotopic And Photopic Vision Revisited
April 25th, 2008 | No Comments »The following text is abstracted from Wikipedia:
“Scotopic vision is the monochromatic vision of the eye in dim light. Since cone cells are nonfunctional in low light, scotopic vision is produced exclusively through rod cells. Vision in normal light with functioning rod cells is photopic vision”.
That “cone cells are non-functional (or shutdown?)…” there is just no experimental evidence for such a statement! One would reason this way if one believed that cone cells are the source of color…which they, clearly in this explanation, are not! “Scotopic vision is produced exclusively through rod cells”… how on earth? …invoking what mechanism? Scotopic and photopic vision are therefore presented as two separate systems. What physical evidence is there for this statement? From the viewpoint of my geometric explanation all of this is completely erroneous and leads one down the wrong path of thought… and has done so for years and years, i.e., the fallacy that “cones detect color and rods black and white”! It attempts to explain phenomenologically the behavior of the vision process but, in fact, uses the completely wrong mechanisms.
There is really only one system, but, if one must use these terms these are the proper definitions:
Scotopic vision: “Under low light level conditions the rod receptors of the peripheral retina are linked together (as experiments show) to act as a “wide angle light meter” with the exact short wavelength limit of visual response (~400 nm) controlling pupillary constriction, dilating the pupil of the eye and admitting the maximum amount of light to the retina. Under these conditions light intensities of the three primary RGB wavelengths falling on the the retina are insufficient to activate the “Land color mechanism”, i.e., there is insufficient intensity incident on either side of the geometrically determined mid-band (550 nm) reference point at 7-8 degrees of retinal eccentricity to allow a ratio to be obtained and the hues of color perceived. The historic misconception that “rods detect black and white” is explained.
Photopic vision: “Under normal daylight levels of illumination the three primary RGB light intensities abstracted by the retina are sufficient to activate the “Land color mechanism” as defined above and the image including the hues of color is perceived. The peripheral rods, as above, constrict the pupil controlling the intensity of light entering the eye to levels that will not damage the retina”.
There is only one “system”!
GCH
4/25/08
