A Science for Everyone, Community

On polarized lenses.

I recently got a pair of polarized prescription glasses, and have been amazed by how much better I am able to see the world, particularly when driving in the morning and evening, confronted by people’s bright headlights.

While they do make my world noticeably dimmer, they bring out many small details, and seem to make colors more intense – I find myself able to discern grass stalks and foliage from much further ranges than I used to be able to. I suspect it’ll help with spotting wildlife as well.

It’s important to realize that not all glasses claiming to be polarized are – many cheap lenses claim to be polarized, while merely being tinted. If a lens is truly polarized, it will block out a portion of polarized light, meaning light that vibrates more in a certain direction. What portion of light is blocked out depends on the lenses’ orientation.

The lenses on most glasses are polarized to filter out horizontally reflected light, i.e. from puddles on roads, or from bodies of water, plastic, or a well-maintained car. Meanwhile, light reflected from bare metal generally won’t change its polarization. Here’s a link explaining the physics, and explaining what makes light polarized or unpolarized.

If you’d like to check if sunglasses that claim to be polarized are genuine, you can take two pairs of them, place them so their lenses overlap, and rotate them until they are perpendicular to each other. This should noticeably darken the view through the lenses, as you are filtering out most of the incoming light.

Alternatively most laptop screens are linearly polarized, so rotating a pair of polarized lenses in front of one should have a clearly bright orientation, where nearly all light emitted from the screen passes through the lenses successfully, and a clearly dark orientation (about perpendicular to the bright orientation) which blocks out nearly all the the light emitted from the screen.

The polarized lenses, aligned to allow all light emitted by the polarized computer monitor to pass through.
Nearly aligned to filter out all incoming polarized light,
but not quite, so some light still passes through the lenses.
Perfectly aligned, and now all the polarized light emitted from the screen is blocked by the lenses.

As a side effect of filtering out horizontally reflected light, my new lenses should help block out reflections from bodies of water, meaning I should be able to see fish moving beneath the surface of the water. Here’s a video showing the effect of looking through polarized lenses at water. Looking forward to getting out there, and seeing how efficient that is.

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