|WikiProject Medicine / Ophthalmology||(Rated Start-class, Low-importance)|
I think that the simulation image is physically inaccurate - most (all?) LCD screens are setup with the polarization axis at 45 degrees to the vertical (though which side of vertical varies between screens). This is also true for pocket calculators. Yet the simulation picture shows the polarization axis aligned horizontally (the blue bits give the direction of the E field polarization). A.C. Norman (talk) 20:19, 17 March 2009 (UTC)
iMAC screens are horizontally polarized (still not vertical), but I agree having the brush at a 45 degree angle would be much more helpfull — Preceding unsigned comment added by 22.214.171.124 (talk) 13:10, 22 October 2012 (UTC)
If you're testing someone to see if they can really see it, it's good that the diagram is vertical because they won't know which way to claim it's tilted unless they really can see it, so I think it's fine as it is. Djvyd (talk) 18:10, 25 October 2012 (UTC)
Hm, I cannot see the simulated Haidinger effect in the current Wikipedia simulation picture. --Abdull 11:19, 5 August 2006 (UTC)
- It's there. It's in the center of the picture, in the white area to the left and slightly above the word BROWSE, oriented with the yellow brush vertical.
- The real Haidinger effect is pretty hard to see (are you able to see it?) and so is the simulated effect. It's likely that it's more or less visible depending on your monitor settings. Dpbsmith (talk) 13:57, 5 August 2006 (UTC)
- It is very subtle. I generally cannot see it straight-off, but if I look at a blank white LCD screen and tilt my head from side to side, I notice the brush pattern moving with the motion of my head. I can see the yellow nodes quite clearly, but the blue nodes aren't quite as clear. --Mdwyer 22:22, 5 August 2006 (UTC)
- Thank god for this article! I was about to RMA my monitor! --Generalmiaow 22:58, 24 October 2006 (UTC)
Can we add the size Haidinger's brush takes up on ones field of view? I calculated about 3 degrees for the yellow part and me, but I'm not sure if I'm even seeing that thing properly. Comments? Peter S. 17:16, 2 June 2007 (UTC)
- How do you see this brush? Is it everywhere on the screen? --HappyCamper 17:37, 2 June 2007 (UTC)
I had never heard of this, opened up a terminal with a white background, maximized it, and saw this instantly (the yellow, anyway). I am equally likely to believe it as I am to believe I was psyched into seeing it. It doesn't "rotate" with my head, after a certain amount of rotation, it jumps 90 degrees. So, is that it? If so, mention it in the article, which makes it sound like it rotates smoothely. JoshNarins (talk) 23:37, 25 December 2008 (UTC)
I find that I can only see a hint of it on a computer screen (a slight yellowness at my centre of vision) until I rotate either my head or the screen, but by using rotations of 90 degrees and staring at the screen for a few seconds each time before rotating back again, the effect becomes dazzlingly clear - I suspect it's being amplified by the cones becoming temporarily less sensitive to the colour they've just been exposed to, the part of the retina that was seeing yellow thereby getting a much enhanced blue after the 90 degree rotation when more blue and less yellow is detected. The same technique works in the sky, allowing me to see the blue clearly on top of the blue of the sky, which was a big surprise. In reply to JoshNarins above though, I don't see it jumping if I rotate my head or the screen slowly - it stays at a constant angle across the screen throughout any rotation. Djvyd (talk) 18:25, 25 October 2012 (UTC)
Sublety not effective
I have been able to see this effect for some time now, both in the sky and on LCD displays, after an article about it appeared in Sky and Telescope magazine. I am also an "expert" video observer. Even on my properly-adjusted display, the "Simulated appearance of a computer screen" is impossible to discern -- the actual effect is, in fact, more easily visible. For that reason, I recommend removing it or exaggerating it to become more visible. algocu (talk) 22:49, 14 February 2008 (UTC)
Xantophylla is the responsible of the Brush...
I think that a very important thing to point out is that H's brush is mainly due to xantophylla visual pigment. Human vision in based upon four visual pigments: lutein (viz xantophylla), heomoglobine, ferrohemoglobine and ferrihemoglobine. The first one has three particular features we are interested in:
1) absorbs in the blue range of spectrum 2) Has a very anisotropical shape (it's a rod...); radiation stimulates both electronic states and
molecular vibrational states, which are mainly disposed along with the molecule direction. That means that xantophylla is sensitive to the polarization of the light.
3) Xantophylla pigments tend to be parallel to visive nerves; these, because of the fact that fovea
is not flat, are almost orthogonal to the fovea in its central part, and nearly parallel in its outern region. This means that two different areas of the fovea are mainly sensible to two different degrees of polarization.
Point 1) tells us that H's brush should be visible in the blue/violet spectral range.
I noticed a few errors with the pigment names.
I changed xantopylla to xanthophyll. I think that was what the article meant. If there are any objections it can be easily changed back.
I see a few errors in this sentence:
Haidinger's brush is entirely due to peculiar features of one of the four visual pigments human vision is based on, that is xanthophylls (also known as lutein, the others being hemoglobine, ferrohemoglobine and ferrihemoglobine).
I don't think that xanthophyll pigments are the visual pigments. (maybe their metabolites are).
Hemoglobine (and its erroneous rivals) is not a xanthophyll pigment, nor a visual pigment, it is the oxygen carrying pigment in vertebrate blood.
The xanthophyll pigments are (lutein, zeaxanthin, neoxanthin, violaxanthin,α- and β-cryptoxanthin). —Preceding unsigned comment added by Dursty (talk • contribs) 03:01, 28 September 2008 (UTC)
This is not a very convincing proposed mechanism and borders on the fanciful. At the level of a single molecule, pretty well EVERY pigment absorbing in the visible spectrum is anisotropic. In order for this microscopic anisotropy to manifest macroscopically then there would need to be a net alignment of pigment molecules both within single cone cells (perhaps possible) and also between the various cone cells within the macula (very hard to imagine given the spatial relationships between the various cone types).
My understanding of this phenomenon is that the effect should be parallel to the direction of polarization for linearly polarized light, but should be fixed to the viewer's eye for circularly polarized light. For this reason, in the case of an LCD monitor you should not expect the effect to "rotate" when you tilt your head, but rather be fixed to the screen. Can anyone confirm this is correct, and fix the confusion in the article? (I'm not an expert) Meekohi (talk) 05:37, 25 February 2009 (UTC)
I seem to remember that the reason for naming the phenomenon "brush" is not that it resembles one (it doesn't). The name is an incorrect translation of the German name, Büschel, which does mean brush now but meant "sheaf" in Haidinger's day. Could someone check it? 126.96.36.199 (talk) 21:58, 22 November 2010 (UTC)
- Using Google translate on the German Wikipedia article gives Haidinger's tufts. Rmhermen (talk) 16:12, 24 June 2011 (UTC)
Seeing it against the sky
..."With practice, it is possible to see it in the naturally polarized light of a blue sky. ".
This is quite true, BUT it needs to be added that the naturally polarized part of the sky is the great circle (or part thereof) that is perpendiculr right angle to the sun. For example, at sunrise/sunset, the polarized part is the meridian. Old_Wombat (talk) 07:48, 29 September 2011 (UTC)
Haidinger's brush is usually attributed to the dichroism of the 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.
this xkcd item mentions that humans can see polarization and the graphic it uses seems to work pretty well. I wouldn't have found this page without having tried it. EdwardLane (talk) 10:48, 20 August 2012 (UTC)
- Thanks! But I don't think the "blue-sky sprites" mentioned here are the same as Haidinger's Brush. The page says that they are caused by white blood cells in the retina, but that's not how Haidinger's brush is formed. Kortoso (talk) 21:33, 15 April 2016 (UTC)
"How I first saw HB".
I was not able to see the Brush no matter how hard I tried, until we went to Questacon (a sort of science museum) in Canberra (ACT, Australia). They have a display there precisely for this purpose - a white screen illuminated by a floodlight in front of which is a rotating polariser. With this apparatus, the Brush is trivially easy to see as it rotates. Most importantly, first and foremost, it confirmed that I COULD see it, and it also gave me an idea of what (angular) size it is, the colours of it, and the expected difficulty of seeing it. After this ... I can now see it very easily.
If you bring up Paintbrush with its default empty white image, and move the mouse cursor to roughly the centre of it, it gives you something to stare at whilst you rotate your head. I have found this background to be very good for seeing the brush. — Preceding unsigned comment added by 188.8.131.52 (talk) 05:17, 14 August 2016 (UTC)
Double the visibility!
When you have two monitors, phones, etc (preferably equal brands), and one of them is rotated 90°, look alternatively to white areas on either one. When your eyes get used to the blue and yellow from looking at one monitor (even if you still can't discern it), looking at the other one duplicates the effect. This is because those areas on your retina which are now slightly desensitized to blue are now seeing "yellow minus blue", and vice-versa. Not only are the colors more prominent, the contrast between the colors is too. --Zom-B (talk) 08:58, 28 September 2016 (UTC)