There is a subtle indicator that tells you whether or not you’re seeing polarized light, and which direction the light is polarized on. Find out about Haidinger’s Brush.

Polarization of light has come in handy over the last few years. Light travels in waves, like the kind you would see traveling along a suspended piece of string if you pulled one end rapidly up and down. Most naturally-emitted light waves are oriented every which way – the crests and valleys can be oriented up and down, side to side, or at any diagonal angle.

Polarized light, on the other hand, has all its waves oriented only one way. Light can be polarized when it reflects off something, refracts through something, or it can be emitted already polarized. One of the easiest ways to polarize light is just to make it go through slits oriented perpendicular to the direction that you’d like light to be polarized. All the light that’s oriented in the wrong direction will be blocked as it tries to get through the slit. Many pairs of glasses are covered with a coating with tiny, imperceptible slits which do just that.

Windshield and sunglass makers use polarization a lot, to make lenses that reduce glare. When light reflects off water or snow, or the horizontal surfaces of cars, much of it is polarized horizontally. The reflection of a lot of sun makes the surface look like a giant sheet of light which drowns out all the light around it. By making glass with a coating that polarizes light vertically, most of the horizontal glare is choked off, allowing the person behind the glass to see more clearly.

Movies that use 3D use polarization as well. They film the movie from two different angles, present one angle only in horizontally polarized light, and one in only vertically polarized light. By making the audience wear glasses, one lens of which only allows vertical light and the other only allows horizontal light, the movie presents two different images, which the viewer’s brain interprets as one three dimensional image.

One of the advantages of polarization is human’s lack of perception of it. Some animals can differentiate between light polarized in different directions, but for humans it’s just a handy way of filtering out a certain percentage of the incoming light without changing the perceived image.

OR IS IT?

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We all know the routine with super powers: a mutated gene, alien origin, or a magic object are required, and usually some cataclysmic family event for motivation. Matt Murdock, better known as Daredevil (and hopefully never again known as Ben Affleck), lost his sight to an accident with a truck carrying radioactive muck. The incident heightened the rest of his senses, which allowed him to use a small radar device and super hearing to allow him to “see.” But guess what? We don’t need a tiny radar, super senses, or even a death in the family to see with sound. We normals can do it already.

How, you may ask? Pretty much just like Daredevil (or bats, or dolphins) do, by bouncing sounds off the environment and listening for the echoes. Blind people have been doing something similar to this instinctively, usually describing how they can “feel” a nearby obstruction like a wall or door. What they’re actually doing is hearing the changing sound of their footsteps as they approach the obstacle. A recent study led by Spanish researcher Juan Antonio Martínez at the University of Alcalá de Henares tested a series of different sounds and techniques designed to teach people how to use echolocation for their own ends. The most effective sound we can make, they discovered, is clicking sound of the tongue pulling away from the roof of the mouth.

“The almost ideal sound is the ‘palate click, a click made by placing the tip of the tongue on the palate, just behind the teeth, and moving it quickly backwards, although it is often done downwards, which is wrong,” Martínez said in a press release.

Normals, bereft of super senses as we are, must resort to gumption and stick-to-itiveness to actually learn how to echolocate effectively. Martinez said students needed two hours a day for two weeks to learn to tell when an object is in front of them, and a few more weeks to be able to identify trees and pavement. A 2000 study found that listeners in motion are able to take advantage of the Doppler effect to locate objects more effectively.

Then again, when there’s a powerful need to learn how to echolocate well, it can be done with astonishing virtuosity. Ben Underwood, who died just last month, became blind at the age of two from cancer. He learned to rollerblade and play Foosball just through sounds and echolocation (the video is pretty amazing). He walked down the street making just the sort of clicks Martinez recommended, and he could tell parked cars from fire hydrants from plastic garbage cans.

So for those of us who didn’t manage to get bitten by a radioactive puppy or hail from a distant asteroid orbiting a purple sun, there’s hope yet! Seeing with your eyes closed is a pretty nifty superpower we can all have… with a lot of practice.