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Quick Questions takes you on a trip with a photon to explain what polarized light is, and how some sunglasses can filter it out to spare you the glare.
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Remember the last time you were smacked in the face by glaring summer sunlight reflected off a lake, or maybe cars in traffic?

Polarized sunglasses are great for blocking that light, but they don't really make anything else that much darker. To understand how they work, you need to understand what polarized light is.

And for this, it helps to remember that light behaves both like a particle and a wave. Light particles, sometimes described as packets of light, are photons. And as photons fly from the sun to your eye, they also vibrate up and down, or side to side, or in any random direction in between, shaking as they travel so that the paths they make look like waves.

Now, all of these flying light particles oscillating in different directions at once together create a big tangle of light waves as they come streaming toward you. This tangled up natural light, like most direct light you're exposed to, is unpolarized. That just means that those photons aren't all oscillating in the same direction or toward the same pole at the same time.

But, this light can untangle itself pretty easily. Those light particles just have to strike something and they'll start vibrating in the same direction. Specifically, when unpolarized light strikes an object, like the surface of a lake or the hood of a car, all the photons start vibrating in the direction that's perpendicular to that surface.

So, light particles that bounce off a horizontal surface, like a highway or a body of water, will begin oscillating vertically. Now, instead of being a tangled up, unpolarized, hot mess, those reflected particles suddenly have fallen into sync. They're polarized- oscillating in the same direction.

So, the glare that you see on bright days on lakes and highways and bright white picnic tables is mostly made up of vertically polarized light. It became polarized when it hit that horizontal surface and its reflected light particles are vibrating straight up and down as they come to you, which brings us back to polarized sunglasses.

The thing to remember here, is that that's a stupid name. The lenses themselves are not polarized, that's not really a thing, and the lenses don't cause the polarization of any light. We only call them polarized lenses because they filter out polarized light. And they do it by blocking any light particles that are oscillating vertically while letting all other light in any other directions through.

You can think of them like little windows covered with horizontal bars. Any particle that's bouncing up and down as it approaches the lens is going to run into those bars and get blocked.

These lenses can function in lots of different ways, but the first sunglasses for polarized light were made in 1936 by the guy who started the Polaroid company, Edwin Land.

He created a filter by suspending millions of tiny molecules of a crystalline compound called herapathite in a clear, stretchy, polymer. Herapathite molecules are shaped like little needles and he used them to, basically, make a barred window on a molecular level.

These days, polarizing filters are made of fancier stuff, but the principle is still the same.

And those filters are what let you drive down a summer road without getting blinded by passing traffic or maybe help you find your glasses after you drop them in a lake. Unless they were your polarized glasses, in which case sorry.

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