Wednesday, August 14, 2013

Haidinger's Brush

Haidinger's Brush is a a visual effect that happens within the eye, an entoptic phenomenon, like floaters.

The effect 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.


Here's another simulation, a lot more subtle than the last. Do you see the fuzzy yellow and blue bow tie floating in the middle of the white space? If you don't see it, tip the computer screen away from you.

Now again, that's just a simulation. Let's see if I can get you to see the "real" illusion. Below this line will be a big area of white space. Scroll down till the white space fills the screen.


Now look toward the center of the white space on the screen, relax your mind, and tilt your head from side to side. Do you see the fuzzy yellow and blue bow tie? If it appears, you may think at first that it is an afterimage from the earlier simulations, but it's the real thing. The colors may switch from blue to yellow and back again as your head tilts.

If you don't see it, try looking at the white screen through polarized sunglasses or a polarizing filter (CPL) from a camera. And if you don't see it at all, don't worry—not everybody sees such effects.

The Haidinger's brush effect is also visible in a blank blue sky, usually 90 degrees to the side of the sun, or at the zenith at sunset. Once you train yourself to see it, you will start seeing it everywhere, and you'll be observing something that's invisible to almost everyone else in the world.
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Previously on GJ:
Floaters
Wikipedia on Haidinger's Brush
Explanation on Polarization.com
The effect is also described in Minnaert's book: The Nature of Light and Colour in the Open Air

12 comments:

June said...

ha... at first I couldn't see the second image. Then I took off my varifocal lenses that have uv filters in them, and there it was!
Just goes to show my glasses are changing what my eyes percieve.

Leslie Hawes said...

I have too many 'floaters' for this to work! :)

Theresa Bayer said...

I'm seeing very pale yellow circles over a blue-grey background. Very very very pale and subtle.

Chris Dunn said...

Fascinating post, I'll keep an eye out for this effect in the sky.

On a slightly unrelated note have a look at this http://www.bbc.co.uk/news/magazine-23536914

This has to be one of the best examples of using natural light without any draw backs.

Deb said...

I've seen this before and wondered what was going on! Glad to have a name for it. But thanks even more for the link to Minnaert's book. I had it in college back in the 1970s but foolishly gave my copy away. As a longtime plein air artist I found it to be quite fascinating.

Katherine said...

I'm with Leslie... I could see loads of my floaters too :-( and no bowties.

James Gurney said...

Know what you mean about the floaters. Me too. Don't worry if you can't see the effect. It's really subtle even under the best of conditions. And remember you have to be looking at polarized light. Some video screens are more polarized than others. This effect doesn't happen when you look at white paper.

Steve said...

"..relax your mind, and tilt your head from side to side..."

I'm told by my Very Significant Other I looked mildly demented while following these directions. Explaining I was looking for the fuzzy yellow and blue bow ties in a pure white screen did nothing to dispel that perception.

I'm imagining thousands of people all over the world, tilting their heads from side to side, their minds obviously relaxed, as their Partners in Life look up from their coffee, wondering how worried to be...

Erika Baird said...

Huh, I can see it when my head's tilted, but when I go right-side up again, it fades away. Very interesting, either way!

Erika Baird said...

Huh, I can see it when my head's tilted, but when I go right-side up again, it fades away. Very interesting, either way!

Timon Sloane said...

Question - do you ever include this effect in paintings intentionally to simulate the sensation of natural polarized light?

James Gurney said...

Timon, no, I haven't included it in any paintings. I only learned about it a couple days ago, and I'm not sure it would make sense to a viewer.