Light pollution becomes a polarizing issue

Polarized light -- the kind of reflected light polarized sunglasses reduce -- has serious effects on creatures who use it but get bamboozled by polarized light reflecting off of engineered surfaces.

György Kriska
Sorry, wrong nursery: A stonefly, lured by polarized light reflected from polished granite, lays her eggs on the granite, instead of in a stream, where they belong.

Light pollution increasingly is seen as a serious problem for wildlife, a point noted by colleague Eoin O'Carroll in early December when he riffed on the topic over at The Bright Green Blog. Typically, this light pollution appears at night, when humans light up their world.

Now, it appears, it's a 24-7 problem. In the January issue of the journal Frontiers of Ecology and the Environment, a team led by Gabor Horvath  a scientist at the Biooptics Laboratory at Eotvos University in Budapest, makes a plausible case that polarized light -- the kind of reflected light polarized sunglasses reduce -- has serious effects on creatures who use it but get bamboozled by polarized light reflecting off of engineered surfaces.

Indeed, according to the team, "we introduce the term 'polarized light pollution' as a new kind of ecological light pollution."

Yes, polarized light comes from "natural" sources such as sunlight reflected off of oceans, lakes, or rivers. A wide range of insects, animals, even fish have adapted themselves to use this polarized light.

But polarized light also reflects off of smooth, dark building materials like polished granite. It also glances off of black plastic sheets, a dark paint job on that '57 T-Bird or Prius,  open ponds of oil or chemicals, and even light reflected off of asphalt roadways and polished black tombstones.

In effect, the "unnatural" polarized light from these and other human-made sources lead creatures big and small -- and the critters that eat them -- in fatal directions. They identify as safe "habitats" or breeding areas that are anything but. They mistake floating plastic for prey. Or their navigation systems go haywire as they try to migrate.

Researchers have noticed, for instance, that insects attracted to vertical panes of glass via polarized light also draw the birds that feed on them. Depending on the bird species, say, magpies, such congregations of smaller birds could attract these scavengers as well. For these larger birds less picky about what's on the menu, why stop at eating bugs when nests near the impromptu feeding station could present an opportunity to prey on any chicks in the nests.

Oil spills provide a less-speculative example. The team notes that polarized light from the sheen in oil spills has attracted insects that fail to escape the muck. The struggling insects attract insect-eating birds and bats, which in turn attract meat-munching predators such as owls or hawks. Everyone winds up stuck or worse.

The team suggests that this polarized-light cascade might have contributed to the pile-up of now fossilized Pleistocene animals at the La Brea Tar Pits in L.A., among other natural tar seeps.

As with other forms of light pollution, relatively modest changes could blunt the effects of polarized-light pollution. These approaches -- from using light-colored materials where reflective surfaces are unavoidable to using matte-like surfaces and altering lighting schemes for parking lots and buildings -- become especially important if structures have streams, rivers, or lakes in their vicinity, the team says.

Video: Using a polarizing filter to reduce the glint from an car.

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