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Encyclopedia > Dark adaptation

The Purkinje effect (sometimes called the Purkinje shift, or dark adaptation) is the tendency for the peak sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels. This article refers to the sight organ. ... For other uses, see Blue (disambiguation) Blue is one of the three primary additive colors; blue light has the shortest wavelength range (about 420–490 nanometers) of the three additive primary colors. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... For the act of supplying light to an area, see lighting. ...


This effect introduces a difference in color contrast under different levels of illumination. For instance, in bright sunlight, geranium flowers appear bright red against the dull green of their leaves, but in the same scene viewed at dusk, the contrast is reversed, with the petals appearing a dull red against paler green leaves. In visual perception, contrast is the difference in visual properties that makes an object (or its representation in an image) distinguishable from other objects and the background. ... Prism splitting light Sunlight in the broad sense is the total spectrum of electromagnetic radiation given off by the Sun. ... Geranium can be: The genus Geranium of flowering plants, usually called the cranesbills Any of the garden plants called geraniums, which are members of the related genus Pelargonium. ... Wildflowers Flower (Latin flos, floris; French fleur), a term popularly used for the bloom or blossom of a plant, is the reproductive structure of those plants classified as angiosperms (flowering plants; Division Magnoliophyta). ... Look up green in Wiktionary, the free dictionary. ... In botany, a leaf is an above-ground plant organ specialized for photosynthesis. ... Dusk in Breaux Bridge, LA. Dusk or civil dusk is the time at which the sun is 6 degrees below the horizon in the evening. ... A petal is one member or part of the corolla of a flower. ...


In visual astronomy, the Purkinje shift can affect visual estimates of variable stars when using comparison stars of different colors, especially if one of the stars is red. Astrometry: the study of the position of objects in the sky and their changes of position. ... Most stars are of nearly constant luminosity. ... The Pleiades star cluster A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. ...

Contents


Physiology

The effect occurs because the color-sensitive cones in the retina are most sensitive to yellow light, whereas the rods, which are more light-sensitive but do not distinguish colours (and thus are more important at dusk), respond best to green-blue light. This is why we become virtually color-blind under low levels of illumination, for instance moonlight. Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Cone cells, or cones, are cells in the retina of the eye which only function in relatively bright light. ... Human eye cross-sectional view. ... Yellow is a color with a wavelength 565-590 nanometers. ... Normalised absoption spectra of human rod (R) and cone (S,M,L) cells. ... Moonlight has several meanings: Moonlight is the light that is perceived as coming from the moon. ...


History

The effect was discovered by Johannes Evangelista Purkinje. Purkinje was a polymath who would often meditate at dawn during long walks in the blossomed Bohemian fields. Purkinje noticed that his favorite flowers appeared red on a sunny afternoon, while at dawn they looked bluish-red. He figured that the eye has not one but two systems adapted to see colours, one for bright overall light intensity, and the other for dusk and dawn. Jan Evangelista Purkinje (also spelled Purkyně) (1787 - 1869) was a Czech anatomist, patriot, and physiologist. ... Renaissance man links here. ... Bohemia This article is about the historical region in central Europe; for other uses, see Bohemia (disambiguation). ...


See also

An optical phenomenon is any observable event which results from the interaction of light and matter. ...

External link


  Results from FactBites:
 
Webvision: Light and Dark Adaptation (2369 words)
Dark adaptation forms the basis of the Duplicity Theory which states that above a certain luminance level (about 0.03 cd/m2), the cone mechanism is involved in mediating vision; photopic vision.
When the same size test spot is used in the peripheral retina during dark adaptation, the typical break appears in the curve representing the cone branch and the rod branch (figure 5).
With dark adaptation, we noticed that there is progressive decrease in threshold (increase in sensitivity) with time in the dark.
RPB - Research to Prevent Blindness (1989 words)
Dark adaptation is the recovery of light sensitivity by the retina in the dark after exposure to an intense light.
Alterations in dark adaptation may be detectable before lesions become visible in the fundus because dark adaptation is highly sensitive to alterations in the retinoid cycle.
The dark adaptation data is fit by a nonlinear regression model to estimate the kinetic parameters of rod-mediated and cone-mediated dark adaptation.
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