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Polarized Sunglasses: How Do They Work?

Polarized lenses are the greatest invention since sliced bread. Polarized lenses were invented in 1936 by Edwin H. Land. This is the same Edwin H. Land who introduced you to the Land's camera by Polaroid. They have been a staple in eyewear for decades. It's a good thing, too. Polarized lenses reduce the danger of glare from flat surfaces like asphalt, glass, or water. This article will answer the question: How do polarized sunglasses lenses work?


Polarized Sunglasses Explained

Let's first look at the history of the Polarized Lens. In 1808, Etienne Louis Malus, a French mathematician and physicist, discovered that light waves from sunlight, which vibrate in all directions, could be aligned in one direction if they are reflected off something.

This is why it's helpful to see light as a knuckleball. The ball leaves the pitcher's hands and travels in one direction. However, it is weaving and bouncing left and right, completely erratic, and looking like an uncontrollable bundle of energy. If the bat connects well, the ball will fly back, spinning gracefully and without any of the erratic motion.

The same thing happens to light reflected off horizontal surfaces. It loses its erratic motion, and instead travels in one concentrated beam with horizontal motion. This is what we call glare.

For a moment, let's pretend that reality is not real. However, we can still use the metaphor of a baseball to show that the ball hit by the batter is still moving in one direction but it's also moving from side-to-side. The ball is quickly approaching the outfield fence which is made up of a series vertical bars. The ball weaves left and right as it approaches the outfield fence. It bounces off the posts because it cannot pass through the horizontal zig-zagging lines.

The same ball could pass through gaps in fences if it were to travel vertically, moving up or down, instead of in the horizontal line that the bars are in.

It may help to picture light as a mattress you are trying to squeeze through a door. It's impossible to fit the mattress through a doorway if it's perpendicular to it. If you flip the mattress upside down, it will pass through the doorway easily.

This is your polarized filter for sunglasses.

The filter will block any horizontally traveling light (e.g., the glare off water or the sun) that has been polarized by reflection when the polarization axis of the filter is vertical. Because it is moving in the opposite direction to the filter, it cannot pass through.

The filter will also block horizontal light, so any non-polarized light moving in multiple directions (e.g., the knuckleball), will become polarized when it passes through.


How to test if your lenses are polarized

You could reduce the light passing through if you took 2 filters and placed them parallel to each other. Vertical light will be blocked by the filter with a horizontal orientation, while horizontal light will be blocked by the filter with a vertical axis. If you take two polarized lense and tilt them between 0deg to 90deg angles, the lenses will darken as they rotate.

By holding your lenses in front of an LCD backlit screen, you can verify that they are polarized. The lens should get darker as you turn it. Because LCD screens have crystal filters that rotate the polarization axis as light passes through, this is possible. The liquid crystal is usually sandwiched between two different polarizing filters, at 90 degrees from each other. While this is not a standard practice, most polarizing filters for computer screens are at a 45-degree angle. In the video, the filter is on a horizontal axis. This is why the lens doesn't darken until it is fully vertical.


Protecting your eyes from the summer sun

While outdoor enthusiasts are familiar with ways to protect their skin from sunburn, a little preventative eye care can make a big difference. These simple tips and insights will help you protect your eyes from any potential damage.

All sunglasses are not created equal. While cheaper lenses allow less light to your eyes, they don't block the UV rays that you can't see. Your eyes can be permanently damaged by UV rays. Make sure that your lenses block 100% of both UV-A rays and UV-B radiation. UV-A and UVB rays can penetrate the protective ozone layer and cause permanent damage to your eyes.


Are polarized sunglasses better for your eyes?

It's not exactly. They do not offer additional protection against UV light. However, they can increase contrast which can be dangerous or distracting in situations. Its glare-reducing properties can help to reduce the risk of sun-induced strain and headaches.


What are some of the drawbacks to polarized sunglasses?

Polarized lenses can make it hard to view LCD screens, which is the most common disadvantage. Polarized lenses reduce light that your eyes receive from an LCD screen by reducing the amount you see. Your phone screen may not be visible if you look at it from a 90 degree angle. However, changing angles can cause the display to disappear completely.

Can polarized lenses be used for driving? It is not for everyone. Polarized lenses can make it more obvious that automotive glass, which can cause minor distractions while driving.