Why Using A Cell Phone To See In Bad Weather Actually Works

A video of two people driving through torrential rain in China is going viral this week due to the way they’re able to see the road through the weather. Thanks to a little thing called physics, you can indeed see the road better in a storm through a cell phone camera than your own eyes, but I still wouldn’t recommend it.

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The video comes to us from China (though we initially caught it on Reddit’s InterestingAsFuck board) where Typhoon Gaemi is walloping the mainland with storms. At least 22 people have died in the deluge so far, according to Al Jazeera. To keep from adding to that death toll, two enterprising folks driving down a motorway in China figured out a neat way for the passenger to keep the driver updated on problems on the hazy roadway: They used their phone camera to see through the rain. But how, exactly, does this work?

Gather ’round children, and learn some science.

Stop me if you’ve hear this one, but light is an electromagnetic wave which means it oscillates in all directions. Such spinning light is called unpolarized light, as it hasn’t been forced into a single direction. It becomes polarized when it hits something. This is seen as glare on say, a windshield, the sparkle on a body of water, or the scattering of light by a gazillion water droplets all at once during a storm. In order to cut down on the visual noise of polarized light, you can use a lens that has been polarized—or has been manufacturer in such a way as to only let in light traveling in a single direction. Here’s how it works in Polarized film (invented by the man who would later found Polaroid) according to Harvard:

One way to polarize light is using a polaroid film. The first such film was invented by Edwin Land in 1928, while an undergraduate at Harvard. He came up with a way to align polymer molecules in a thin sheet into long needlelike strands. When an electric field acts on the electrons in those strands, it can only move the electrons up and down in the strand direction, but not perpendicular to the strands. Thus the only polarization which can pass through is linearly polarized in the direction perpendicular to the strips.

Think of it like the bars on a prison cell. Some of the inmates can slip through the bars and escape to hit your eye, but the wilder ones that move in different directions than the bars can’t. This video has a great example of how polarizers work:

Polarized Light

Cell phones have such a polarizing filters built in. While it might not be enough to make your car photography pop, a cell phone’s polarizing filters are enough to only let some of the light coming in, allowing the passenger to see more of the road than their human eyes could make out alone.

Phones aren’t special. A much safer option would be for the driver to be wearing sunglasses with polarized lenses, or even a polarized window tint. Polarization is so common on sunglasses that polarizing windshields out of the factory isn’t really done by automakers, as the two polarizations can cut down on light to a dangerous degree. Some cars with projected heads-up displays, like Audi, run into the problem of their windshield readouts not showing up to drivers with the sunglasses due to double wammy polarization.