Picking sunglasses: how do polarized lenses work?

    Seriously, what the heck does it even mean to buy sunglasses with polarized lenses? You’d think for a feature so common among sunglasses we would have a better idea of how this anti-glare lenses work. As it turns out, there’s a bit of a light physics lesson involved in these shades, but nothing you can’t read over before grabbing your polarized sunglasses  and heading out for, say, a day at the beach.

Light Lessons

    So, the one thing most of us already know, is that polarized sunglasses prevent you from seeing glare, that super bright and concentrated reflection of the sun’s rays. Glare can get pretty annoying when it’s coming from water’s surface, cars or windows on buildings, or even the road itself while you’re driving. When the sun’s rays can do serious damage to your eyes, you’ll want to be sure that the protection of your sunglasses is adequate for these harsher conditions. But, how does glare even happen?

    The folks at HowStuffWorks had the science scoop. When the sun’s rays shine down from the sky, they’re spread out coming downward but at countless angles, across multiple different planes. This light is more diffused. However, when this light comes into contact with reflective surfaces like water, these flatter surfaces concentrate the light into more focused beams, that we see as those pesky bright rays off the top of other vehicles windshields. Imagine the sun’s rays coming to earth as a mist of water from a spray bottle, versus the glare off of a glossy surface which would be more like a concentrated stream from a hose.

All in the Molecules

     Okay, now that we’ve got the light physics down, let’s get to the sunglasses themselves. Polarization is the process of applying a filter to the lenses, usually made of a special kind of PVA plastic. This gets either stuck to the lenses as a filter, or embedded in/mixed into the lens during manufacturing.

    Either way, the science is the same. This special material is processed and applied in a way where the molecules that make it up all point in the same direction. So, when light comes at them from the typically head-on angles that glare does, the molecules all reflect or absorb this light in the same way, like a ball bouncing off a picket fence. Pretty cool, but remember that this also can mean reduced visibility in more poorly made polarized sunglasses, so be sure to try them on and look around first. And one more reminder: there’s a lot of mixed messages and weird lingo floating around the sunglasses section, but expensive doesn’t always mean better protection.