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Encyclopedia > Haidinger's brush
Simulated appearance of Haidinger's brush for vertically polarized light. Size and intensity exaggerated for clarity
Simulated appearance of Haidinger's brush for vertically polarized light. Size and intensity exaggerated for clarity

Haidinger's brush is an entoptic phenomenon first described by Austrian physicist Wilhelm Karl von Haidinger in 1846. Many people are able to perceive polarization of light. It may be seen as a yellowish horizontal bar or bow-tie shape (with "fuzzy" ends, hence the name "brush") visible in the center of the visual field against the blue sky viewed while facing away from the sun, or on any bright background when looking through polarized sunglasses. The direction of light polarization is perpendicular to the yellow bar (i.e. vertical if the bar is horizontal). Fainter bluish or purplish areas may be visible between the yellow brushes (see illustration). Haidinger's brush may also be seen by looking at a white area on many flat panel computer screens, in which case it is often diagonal. Haidingers brush. ... Entoptic phenomena are visual effects whose source is within the eye itself. ... Wilhelm Karl, Ritter von Haidinger (February 5, 1795 - March 19, 1871), was an Austrian mineralogist, geologist and physicist. ... This article treats polarization in electrodynamics. ...

Some arthropods (insects, mantis shrimp), mollusks (cuttlefish, squid, octopuses) and fish are sensitive to polarized light. Orders Subclass Apterygota Symphypleona - globular springtails Subclass Archaeognatha (jumping bristletails) Subclass Dicondylia Monura - extinct Thysanura (common bristletails) Subclass Pterygota Diaphanopteroidea - extinct Palaeodictyoptera - extinct Megasecoptera - extinct Archodonata - extinct Ephemeroptera (mayflies) Odonata (dragonflies and damselflies) Infraclass Neoptera Blattodea (cockroaches) Mantodea (mantids) Isoptera (termites) Zoraptera Grylloblattodea Dermaptera (earwigs) Plecoptera (stoneflies) Orthoptera (grasshoppers, crickets... Families Not necessarily a complete list: Alainosquillidae Bathysquillidae Coronididae Erythrosquillidae Eurysquillidae Gonodactylidae Hemisquillidae Indosquillidae Lysiosquillidae Nannosquillidae Odontodactylidae Parasquillidae Protosquillidae Pseudosquillidae Squillidae Takuidae Tetrasquillidae The Mantis shrimps are the order Stomatopoda of crustaceans. ... Families Sepiadariidae Sepiidae Cuttlefish are animals of the order Sepiida, and are marine cephalopods, small relatives of squids and nautilus. ... Suborders Myopsina Oegopsina Squids are the large, diverse group of marine mollusks, popular as food in cuisines as widely separated as the Japanese and the Italian. ... Families 14 in two suborders, see text The octopus is a cephalopod of the order Octopoda that inhabits many diverse regions of the ocean, especially coral reefs. ...

Haidinger's brush is usually attributed to the dichroism of the pigment of the macula. The brush's size is consistent with the size of the macula. The macula's dichroism is thought to arise from some of its pigment molecules being arranged circularly. The small proportion of circularly arranged molecules accounts for the faintness of the phenomenon. As well, the outer layer of the cones is said to be birefringent; this is thought to contribute to the phenomenon. The cornea has also a slight birefringence. In optics, the term dichroic has two related but distinct meanings. ... In biology, pigment is any material resulting in color in plant or animal cells which is the result of selective absorption. ... Human eye cross-sectional view. ... Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Cone cells, or cones, are cells in the retina which only function in relatively bright light. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the division of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on... The cornea is the curved, transparent layer that covers the front part of the eye and protects its inner structures. ...

Seeing Haidinger's brush

Simulated appearance of a computer screen viewed through a polarizer, showing typical size and intensity of Haidinger's brush

Many people find it hard to see Haidinger's brush initially. It is very faint, much more so than generally indicated in illustrations, and, like other stabilized images, tends to appear and disappear.

It is most easily seen when it can be made to move. Since it is always positioned on the macula, there is no way to make it move laterally, but it can be made to rotate, by viewing a white surface through a rotating polarizer.

To see Haidinger's brush, start by using a polarizer, such as a lens from a pair of polarizing sunglasses. Gaze at an evenly lit, textureless surface through the lens and rotate the polarizer. The accompanying image shows the approximate size of the brush as it appears on a nominal-15" (38 cm) computer monitor located about 18" (46 cm) from the eye. The picture shows the actual intensity of the brush as seen by one observer. Different individuals see it with different degrees of intensity and distinctness, but it is usually very pale.

It appears with more distinctness against a blue background. With practice, it is possible to see it in the naturally polarized light of a blue sky. Minneart recommends practicing first with a polarizer, then trying it without. The areas of the sky with the strongest polarization are those 90 degrees away from the sun. Minnaert says that after a minute of gazing at the sky, "a kind of marble effect will appear. This is followed shortly by Haidinger's brush." He comments that not all observers see it in the same way. Some see the yellow pattern as solid and the blue pattern as interrupted, as in the illustrations on this page; some see the blue as solid and the yellow as interrupted; and some see it alternating between the two states.

Further reading

Alcoz, J. (No date). Haidinger's Brush. San Antonio, TX: Polarization.com. Retrieved June 30, 2004, from http://www.polarization.com/haidinger/haidinger.html

Minnaert, M. G. J, 1993, Light and Color in the Outdoors. (translated by Len Seymour from the 1974 Dutch edition). ISBN 0-387-97935-2, Springer-Verlag, New York.



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