Purkinje effect
From Biocrawler, the free encyclopedia.
The Purkinje effect (sometimes called dark adaptation) is the tendency for the peak sensitivity of the human eye to shift toward the blue end of the spectrum at low illumination levels.
This effect introduces a difference in colour contrast under different levels of illumination. For instance, notice the bright red of geranium flowers against the dull green of their leaves in bright sunlight, and then view the same scene at dusk. The contrast will be reversed, with the petals appearing a dull red against paler green leaves.
The physiological reason for this effect is that the colour-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. For this reason, we become virtually colour-blind under low levels of illumination, for instance moonlight.
In visual astronomy, it can affect visual estimates of variable stars when using comparison stars of different colours, especially if one of the stars is red.
The effect was discovered by Johannes Evangelista Purkinje (born December 17, 1787 in Libochowitz (Libochovice), Bohemia – died July 28, 1869). Purkinje was a real polymath who would often meditate at dawn, in long walks in the blossomed Bohemian fields. Purkinje saw his favourite flowers (that were red) on a sunny afternoon. But at dawn they certainly looked bluish-red only. He figured that our eyes have not one but two systems adapted to see colours, one for bright overall light intensity, and the other for dusk and dawn.
External link
- Detailed account of the Purkinje effect (http://www.iris-ward.com/_HTM/MEIS/P/1576-MEIS.htm)pl:Efekt Purkyniego
