When buying new sunglasses, people commonly ask the same question: Do I really need polarized lenses? As they should. After all, polarization is far from a small investment. For example, a classic pair of Wayfarers with polarized lenses ($203) lists over 30 percent more than the non-polarized version ($153). “The lenses look the same when you see them, but there are physical layers, not just coating layers, in these lenses that take a lot more time to make,” said Dave Barton, the founder of premium eyewear brand David Kind.

Polarized lenses have an immediate effect on vision, reducing glare off of flat surfaces. The quality of material and method of manufacturing greatly affects both the price point and the optics. “A polarized lens in a $10 pair of glasses is going to have some of the properties of a polarized lens in a $500 pair of glasses,” Barton said. “But, you’re getting 30 percent more effectiveness and quality, and maybe 50 to 80 percent more durability when you start going up.”

There are many manufacturers making medium and low-end polarized lenses, but the highest quality glass comes from just a few factories across the world, including Barberini in Italy and Nakanishi in Japan. “When you’re sourcing your lenses, it makes a difference to a point what you’re picking,” Barton said.

To better understand how polarized lenses work, the range of available options and who benefits the most from polarization, we talked to few independent eyewear experts.

Q:

Why are polarized lenses important?

Behle:

We consume a world of reflected light that is constantly moving and in flux. Polarized lenses channel this reflected light, reducing its movement. This channeled light provides more visual clarity and definition. Polarized lenses also address eye fatigue and strain from reflected light. Eye fatigue is caused as your pupils chase reflected light, which causes constant expansion and contraction of the eye as it adjusts to the changing angle and intensity of the light. This eye fatigue is a direct trigger for headaches and migraines.

Barton:

Polarized lenses are almost like mini Venetian blinds — there are microscopic blinds that are in the film in the lens. That cuts out the glare that’s coming into your eyes at that angle. It’s very effective at this.

Q:

What makes them different than other lenses?

Daly and Vallot:

Polarized lenses block reflected light so they offer a higher level of eye protection. People often forget sunglasses are a medical device. Unlike our skin, our eyes do not contain melanin. This means [that] each time we expose them to sunlight, they become more sensitive.

Behle:

Polarized lenses have a polarized film that filters reflected light in a vertical plane (the reflected light is predominately vibrating in a horizontal plane). In channeling that light, polarized lenses remove the majority of electromagnetic vibration, also known as glare.

Barton:

There are many different levels and many different price points. The basic way that it works is the same — it requires a film. There are different quality levels of film where some are more effective than others, but the big difference comes in how the lens is made with that film and how clear the lens is.

Q:

How do factories make polarized lenses?

Barton:

The cheapest way to produce it is to use an acrylic-based material or acetate material, and then laminate the polarized film between these thin sheets of acrylic or acetate. Then they use heat to form it into the spherical shape of a lens and then they cut the lens. Those are the cheapest, but they also have the most distortion of the lens. You can see these hot spots around the edge of the lens that cause distortion and reduce the polarize effectiveness. And they scratch really easily too.

The next level is polycarbonate injection molded [lenses]. You see a lot of this being used. It’s what Oakley uses primarily, and it’s what most of the other sports brands use. It’s an impact-resistant material, and it’s more scratch resistant than the [laminated lenses]. The film is put into a mold and they inject the polycarbonate material around it. That makes for a good strong lense, but it’s not a clear lens to look through. It can cause distortion in the polarized film.

Next, you start getting into CR39, where you have two wafers and you glue the polarized film in between the two wafers of the lens. Done with a high quality, this can be a much clearer lens than the polycarbonate one, but it’s not impact-resistant.

Then you have glass, which is primarily what we use at David Kind. It’s done in the same construction method as the CR39, but it’s going to be the clearest, most scratch-resistant material. It seems to affect the polarization film the least. If it’s manufactured in a high-quality facility, it doesn’t distort the polarized film, so you have nice polarized effectiveness all around the periphery of the lens.

There’s also cast NTX, which is kind of like a Trivex material. Instead of injection molded under pressure, it’s cast into a mold around the polarized film. That results in an impact resistant, relatively distortion-free lens material. So I would say, for sport, that is the best. And for optical clarity and scratch resistance, glass is the best.

Q:

Are there any other differences in low quality polarized lenses and high quality polarized lenses?

Behle:

Quality in a polarized lens starts with the quality of the lens material. The highest quality lenses are optical-grade and they’re predominately made out of CR39 or mineral glass. The second component is the quality of the polarized film and how the film is adhered to the lens and aligned. Quality polarized lenses use a higher quality polarized film, sandwiched between the two lenses so that the film is perfectly aligned in the worn position. They also use a backside anti-reflective coating on the inside of the lens that absorbs light that enters from the back of the lens and prevents this light from reflecting back into your eye. Further, high-quality lenses will use hydrophobic and oleophobic coatings that repel water and oils, to ensure that your lens is clean and clear.

Q:

Can you get a good polarized lens at an entry-level price?

Barton:

One of the best values out there is a glass polarized Ray-Ban aviator. That’s a great quality lens and they’ve been doing it for years. As you move up-market, you start getting into better frames, and you start getting things for the lens like anti-reflective coating, which make a huge difference. You can get into photochromics, you can get into mirror coatings — all of that increase the price as well. When you go down-market, you start going into the polycarbonate materials. The cheapest of the cheap are the gas station polarized ones are the acrylic acetate ones that won’t last.

Q:

What are other alternatives? And who are they appropriate for?

Daly and Vallot:

There are different levels of protection available. Our mountain athletes also request IR (infrared rays) protection due to a closer proximity to the sun. IR causes our eyes to get warmer and inflamed so this additional protection is paramount. Mirrored lenses have also gained a certain notoriety in the sports industry but this is more cosmetic than anything else in our opinion.

Q:

Who should have polarized lenses in their glasses?

Daly and Vallot:

Anyone that wants a heightened level of eye protection ultimately but in particular those who do water sports. The term has certainly been over-marketed in recent years and the quality of polarization varies greatly. A high-quality lens will block reflective light but still allow clear screen (Garmin / iPhone) visibility which is increasingly important to our athletes today.

Behle:

Everyone. It is absurd to be wearing a sunglass, especially a premium sunglass, that does not have a polarized lens. Beyond UV protection and reducing the amount of light that penetrates the lens, which virtually all sunglasses have, the real point of having a sunglass is being able to see clearly and without eye strain in the constant barrage of reflected light. Most people equate polarized lenses with outdoor activities on the water, but they are conducive to virtually all settings. You are getting almost as much reflected light from urban surfaces, e.g. auto windows and concrete, as you are on the water. The mirror effect and movement of water, of course, amplifies this glare.

Barton:

My experience is it’s definitely not for everyone; it’s for most people, but it’s not for everyone. Some people feel a little discombobulated because they’re disoriented by the effects that polarized can have, They’re not used to it. For example, car window screens that have window tint, you start seeing these purple blotches. It can change how you perceive the road surface. If you’re a skier and you want to see the reflection of ice on a sunny day, you don’t want polarized. If you’re a pilot, many of the windscreens are polarized themselves, and when you combine a polarized windscreen and polarized glasses, it can black out the screen, so they don’t wear polarized. It’s definitely not for everyone, but for most people, you’re going to have a better visual experience, especially when you’re in bright conditions, near water or outdoors.