Polarized lenses—the greatest thing since sliced bread. Invented in 1936 by Edwin H. Land, the same man who brought you the Land’s camera by Polaroid, polarized lenses have long been a staple in the eyewear industry. And for a very good reason. Polarized lenses cut hazardous glare off of flat surfaces such as water, glass, and asphalt. The question this article will answer is: how do polarized sunglass lenses work?
Polarized Sunglasses Explained
First, let’s back up a little in the history of the polarized lens. In 1808, a French physicist and mathematician by the name of Etienne-Louis Malus discovered that light waves from the sun, which usually vibrate in all directions, can be aligned in one direction when reflected off something.
One way to understand this is to think of light like a knuckleball. When it leaves the pitcher’s hand, the ball is traveling in one trajectory, but it’s weaving and bouncing up and down, left and right, totally erratic and looking like a bundle of unpredictable energy. But if the bat connects solidly, the ball will go soaring back out, spinning gracefully without any of that erratic motion.
In the same way, light that is reflected off a horizontal surface loses its erratic motion and travels in one concentrated beam in a horizontal motion. This is what we perceive as glare.
Stepping away from reality for a moment, but still using the metaphor of a baseball, imagine that the ball that was hit by the batter is still traveling in one direction, but while moving forward, it’s also weaving from side to side. It’s fast coming up on the outfield fence, which is a series of vertical bars. As the ball approaches, weaving left and right, it bounces off the vertical fence posts, because there’s no way it can pass through moving in a zig-zagging horizontal line.
If that same ball was instead traveling in a vertical line, moving up and down, it could easily pass through the gaps in the fence because it’s in the same alignment as the bars.
For this example, it may also help to think of light like a mattress that you’re trying to fit through a door. If the mattress is perpendicular to the door, there’s no way you’ll be able to get it through, right? But if you turn the mattress upright, it can pass through the doorway without any issue.
This vertical fence is the polarized filter in your sunglasses.
When the polarization axis is vertical, all light that has been polarized through reflection and is now traveling horizontally (such as the glare off of water or a windshield), will be blocked by the filter. It can’t pass through because it’s moving the opposite direction of the filter.
Likewise, any non-polarized light that’s moving in multiple directions (i.e., the knuckleball) will become polarized as it passes through the filter, because the horizontal light will be blocked, and the vertical light will pass through.
How to Test If Your Lenses Are Polarized
If you were to take 2 of these filters and cross them perpendicular to one another, less light would pass through. The filter with a horizontal axis will block vertical light, and the vertical axis will block horizontal light. That’s why if you take two polarized lenses and tilt them back and forth between 0° and 90° angles, they'll darken as you rotate them.
You can also verify whether your lenses are polarized by holding them in front of a back-lit LCD screen. As you turn the lens, it should become darker. This is because LCD screens use crystal filters that can rotate the polarization axis of light as it passes through. The liquid crystal is normally sandwiched between two polarizing filters at 90 degrees to each other. Although not standard, many polarized filters on computer screens are oriented at a 45 degree angle. The screen in the video below has a filter on a horizontal axis, which is why the lens does not darken until fully vertical.
Upgrade to Polarized Lenses
At Revant, we specialize in making polarized replacement lenses for any brand of sunglasses. If you have an old pair of non-polarized sunglasses that need to be refreshed or upgraded, we can help. Check out our full assortment of polarized lenses in the link below.