Throwing light on a mysterious human 'superpower'

March 2, 2015, Institute of Physics
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Most people, at some point in their lives, have dreamt of being able to fly like Superman or develop superhuman strength like the Hulk. But very few know that we human beings have a "superpower" of our own, which almost anybody can perform by simply staring at the computer screen in front of them. As physics teacher David Shane explains in March's issue of Physics World, human beings have an astonishing ability to detect the polarization of light with just the naked eye.

Even though this "superpower" is not on the scale of those paraded by comic book heroes, many of us don't know that this exists and a solid explanation as to why we are able to exhibit the bizarre skill has evaded the science community for centuries.

As Shane explains, the basis for the skill lays in the fact that light consists of electric and magnetic fields that oscillate, or "wobble", on axes perpendicular to each other.

The light that we observe from natural sources such as the Sun is often "unpolarized" – this means that the light waves reaching us all have electric fields that are orientated in many different directions.

Polarized light simply means that the electric fields of all waves are aligned and oscillate on the same axis. Light from the Sun can become polarized in many different ways, like when it passes through special Polaroid filters or bounces off the surface of a still lake.

In 1844 Austrian scientist Wilhelm Haidinger discovered that when somebody looks at the source of they see a distinctive, colourful shape at the centre of their vision.

Known as Haidinger's brush, the shape looks like a small yellow bow tie crossed with a small blue bow tie. The blue bow tie is aligned with the electric field of the observed light, so this can be used to determine the axis of the light's polarization.

In his article, Shane gives hints and tips for the best way to go about seeing Haidinger's brush – a blue or white background on an LCD computer screen is a handy source – and how it serves as an excellent teaching tool in his physics lessons.

In the accompanying video to this month's issue of Physics World, you can test out this "superpower" by trying to detect Haidinger's brush yourself.

Shane also describes the possible explanations for Haidinger's brush, the most recent of which was put forward by a research team led by Albert Le Floch at the University of Rennes in France.

Le Floch et al. hypothesize that the brush is caused by the interaction of polarized light with a type of photoreceptor, called cones, in the human eye. They believe that the rare blue cones in the eye – which are most sensitive to the blue frequency of light – are distributed in such a way that more of the polarized light entering the eyes can be transmitted onto these blues cones, producing the characteristic blue bow tie in our vision.

Finding a use for this special "superpower" has proved difficult; however, Haidinger's brush always appears in the centre of the vision, so it is possible to use it to correct "lazy eye".

But as we celebrate the properties and applications of in 2015 as part of the International Year of Light, Shane declares that this natural talent can be used as a "fun and fascinating piece of physics" that everybody can share.

Explore further: Generating Mobius strips of light: Researchers experimentally produce these structures from light polarization

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poisonoak
2.6 / 5 (5) Mar 02, 2015
After a little practice I definitely see it. But tilting my head to the right versus tilting to the left I get a 20 or 30 degree angle shift in the angle of the pattern. The angle shift is sudden and occurs roughly when my head is straight up. Does that mean my monitor has several polarized light angles?
KBK
5 / 5 (2) Mar 03, 2015
Your LCD monitor has at least one pair of precisely aligned polarization filters.

One horizontal, one vertical.

the LCD 'fluid' itself, which polarizes due to the activation or operational characteristics, is sandwiched between them, on a substrate/grid of glass and electrodes.

The fluid is electrified, and polarizes/aligns,and either blocks or allows light through the given pixel and given color for that pixel, depending on level of electrification (for lack of a better word). The three 'polarizations'..... two passive and one active, is what creates the light pass though -or blocked- effect.
ilya_simkhovich
not rated yet Mar 03, 2015
i think this was in an issue of "mondo 2000" or the "user's guide to the new edge"; i own a copy. that was 20 years ago but it was more about seeing the cross in the sky by using something.
antigoracle
3 / 5 (2) Mar 03, 2015
I saw Jebus!!

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