Beyond human sight

Our eyes contain photoreceptors called cones that allow us to see the colors red, green, and blue. Using just these three types of cones, we can see the entire rainbow of the visible light spectrum. However, different species have different color receptive cells – dogs have only blue and green cones, while seals and dolphins can only see in black and white.

It’s pretty easy to imagine what the world might look like through the eyes of a dog or a dolphin. However, many other species have sophisticated eyes that can see colors and properties of light that our brains have never processed. What do flowers look like through a bumblebee’s eyes, with hidden markings in ultraviolet that humans could never see? How could we possibly imagine what a rainbow looks like through the eyes of a mantis shrimp, a remarkable animal with sixteen different color receptors in its eyes?

Animal vision is not limited only to color, though. Many pollinators, including bees, can sense the polarization of light, which is used for navigation and identifying flowers. While humans can see polarized light, we can’t distinguish its polarization, so it looks the same as any other light. Luckily, due to the wonders of modern technology, we humans can see polarized light for ourselves. We just need to get a little bit creative.

If you look through a polarizing filter and rotate it 90°, you might notice some light changing intensity. That’s the polarized light right there. Rotating the filter changes which direction of polarization is let through, so light that is polarized in one direction gets blocked out or let through depending on the orientation. If you take a picture through the filter at one orientation, rotate it, and take another picture, you will have two pictures that are almost exactly the same, perhaps with subtle (or not-so-subtle!) differences in lighting and reflection. These differences give us insight into the world of polarized light.

For best results, use a nice camera on a tripod with a rotating polarizer attachment. For mediocre results, use your cell phone camera and a steady hand (that’s what I did). If you don’t have a polarizing filter, you could probably get away with using a pair of sunglasses, since most sunglasses are polarized to block the sun’s glare off water.

Using the process above, I ended up with pairs of images that I carefully lined up and subtracted in GIMP. Here’s an example if that’s hard to visualize.

town-hall

The rightmost image is the difference between the other two. It’s pretty clear that the reflection of the sky off the windows is polarized, as even without subtracting the two images, there is an obvious visible difference between them. The striking final image shows where there is polarized light in the scene, in theory leaving the rest black. In practice, I often get some extra white outlines like those in the top left corner because the photos aren’t exactly aligned when I subtract them.

shinycar

I’ve found that cars reflect polarized light in a way that makes beautiful images. The reflection gives the windshield a pearly sheen and highlights the contours of the car in a beautiful iridescent green. If you look more closely you can see other subtle details, such as the silhouettes of overhead branches in the windshield reflection, or the slight green glow of the sidewalk bricks.

church-highcontrast

Here’s another one that I happen to like a lot. The only source of polarized light in this scene is the sky, which provides a colorful backdrop for the silhouettes of the church and trees. However, this image shows more than that. Since it was a windy day, some objects moved in the time between pictures, and the light outlines around the trees and the cloud in the sky reflect that.

These images augment our human vision and allow us to see additional information about the world around us. The sky in this silhouette photo has an interesting gradient from red to blue. As it turns out, the sky is not uniformly polarized, but rather the polarization is directed tangential to the sun. Bees use this property for navigation, and now we have an idea of what they might actually see when they look up at the sky.

Who knows what else we’re missing out on?

Below is a complete gallery for your viewing pleasure.

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