Haidinger’s brush appears on computer screens and blank areas of sky, and it’s caused by the way our eyes respond to polarized light. The apparition looks like two fuzzy bowties, a blue one and a yellow one, overlapping each other at 90 degrees. The rendering above simulates the effect, but it actually appears smaller, about the size of your thumb extended to your computer screen.
Seeing Haidinger’s brush
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.
An option is to use the polarizer built into a computer’s LCD screen. Look at a white area on the screen, and slowly tilt the head (a CRT monitor has no polarizer, and will not work for this purpose unless a separate polarizer is used).
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. Minnaert 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.
Physiological causes of Haidinger’s brush
Haidinger’s brush is usually attributed to the dichroism of the xanthophyll pigment of the macula. In this Fresnel–Arago laws effect, the unguided oblique rays in the cylindrical geometry of the foveal blue cones, along with their distribution, produce an extrinsic dichroism(two-coloured, refers to any optical device which can split a beam of light into two beams with differing wavelengths. Such devices include mirrors and filters). 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.
Haidinger’s brush Uses:
The fact that the sensation of Haidinger’s brush corresponds with the visual field correlate of the macula means that it can be utilised in training people to look at objects with their macula. People with certain types of strabismus may undergo an adaptation whereupon they look at the object of attention not with their fovea (at the centre of the macula) but with an eccentric region of the retina. This adaptation is known as eccentric fixation. To aid in training a person to look at an object with their fovea rather than their eccentric retinal zone, a training device can be used. One such apparatus utilises a rotating polarised plate backlit with a bright white light. Wearing blue spectacles (to enhance the Haidinger’s brush image) and an occluder over the other eye, the user will hopefully notice the Haidinger’s brush where their macula correlates with their visual field. The goal of the training is for the user to learn to look at the test object in such a way that the Haidinger’s brush overlaps the test object (and the viewer is thus now looking at it with their fovea). The reason for such training is that the healthy fovea is far greater in its resolving power than any other part of the retina.
Haidinger’s brush Video:
Haidinger’s Brush and Circular Polarizers (Blue & Yellow)
Note: I forgot to mention it in the video, but the light that comes from an LCD screen is polarized.
I noticed that the 3D glasses I received from a movie displayed a yellow and blue tint when rotated in front of a polarized light source such as an LCD monitor. This immediately made me think of Haidinger’s Brush which then led me to making this quick video to show off the phenomenon.
I am interested in knowing why this blue/yellow tinting is seen both with a polarizer and with the human eye.
Research on Haidinger’s Brush was carried out by Albert Le Floch, Guy Ropars, Jay Enoch, Vasudevan Lakshminarayanan in their paper titled “The polarization sense in human vision.” They postulated that the chemical structure of the pigment in the blue cone cells of the retina as being responsible for Haidinger’s Brush. If this is the case, I wonder why the polarizer would give the same effect?
I thought that maybe the camera would be unable to see this tint shift if it was truly due to the chemical structure of the pigment in the retina of the eye.
Le Floch, A; Ropars G, Enoch J, Lakshminarayanan V (2010). “The polarization sense in human vision.”.