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Bill Sive
August 15th, 2013, 10:16 AM
Sent to me by my optometrist.

Polarized Lenses and How They Work

Polarized lenses are premium sunglass lenses that solve a problem that regular sunglasses cannot -- reflective glare. To understand how polarized sunglasses work, it's time for a little physics lesson. (C'mon it won't be that hard!)

Sunlight and Reflections

Sunlight is emitted in all directions, and individual light waves are somewhat random in their orientation. Light of this type is called unpolarized light.

But when sunlight strikes a flat, reflective surface, the light rays that bounce back from the surface are no longer random in their orientation. Instead, they are arranged in a more orderly fashion and become more uni-directional (polarized). It's this increased organization of these polarized light rays that makes reflections so much brighter than surrounding objects illuminated by direct sunlight.

Regular sunglass lenses reduce the overall brightness of sunlight, but they cannot selectively reduce the excessive brightness of reflected, polarized light. Your eyes will be more comfortable (compared with wearing no sunglasses at all), but you will still see bright reflections and experience glare that can cause eye strain and interfere with your vision.

The Dangers of Reflective Glare

Polarized light bouncing back from flat surfaces can create very bright reflections that are not just uncomfortable -- they can be downright dangerous.

There are three types of glare caused by reflected light:



Discomfort glare. This is relatively mild glare that is uncomfortable but can be reduced or eliminated by simply squinting or shading your eyes with your hands or a wide-brimmed cap.
Disability glare. This is more intense glare that reduces visual acuity and decreases the contrast of objects. It is caused by reflected light that is so bright you feel the need to blink frequently or turn away from the source of the reflection.
Blinding glare. Extremely bright light reflections can be so intense that they cause eye pain and loss of vision for minutes or even days, as in the case of snow blindness.


Glare of any sort can be very dangerous, especially when you are driving, boating, skiing, cycling, running, crossing a busy street, or you find yourself in any situation that may require quick reflexes.
How Polarized Lenses Work

In addition to being tinted like regular sunglasses, polarized lenses contain a very thin filter embedded in the lens material that selectively blocks horizontally polarized light.

Without getting too technical about the molecular structure of this filter, think of it as a tiny window blind with microscopic, linearly arranged slits that selectively block most of the light waves of reflected light and allow light waves of other orientations to pass through.

In doing so, polarized lenses greatly reduce the intensity of light reflecting back from horizontal surfaces, which significantly reduces glare, improves visibility and increases comfort.

Like other high-quality sunglasses, polarized lenses also block 100 percent of the sun's harmful ultraviolet (UV) rays, and they are available in a variety of tints and materials.

Special Advantages of Polarized Lenses

Though polarized lenses provide superior comfort and vision compared with regular sunglasses whenever reflective glare is an issue, perhaps the most dramatic advantage occurs on the water.

Polarized lenses can significantly improve your enjoyment of fishing, for example. By eliminating glare caused by sunlight reflecting off the surface of the ocean, lake or stream, polarized sunglasses enable you to see deep into the water. This is a huge advantage when it comes time to land that prize fish.

Polarized lenses also are great for relaxing on the beach and for locating shells, colorful pebbles (or the occasional sharp rock or piece of glass) in shallow water near the shore.

How Can You Tell if Your Sunglasses Are Polarized?

You can verify that you are wearing polarized sunglasses by performing this simple exercise:



On a sunny day, find a horizontal surface that is highly reflective. (Water in a calm swimming pool is a good choice, or the windshield of a parked car.)
Remove your sunglasses with both hands (one on each temple of the frame) and hold them several inches from your eyes. From this distance, look through the lenses at the reflective surface.
Now rotate the frame so the right lens is directly above the left, and then rotate it back so the two lenses are side-by-side again. Do this several times.


If the lenses are polarized, you'll see a very noticeable drop in the intensity of the reflected light when the lenses are side-by-side (in the normal orientation for wearing), and a significant increase in the brightness of reflections when the frame is rotated 90 degrees (right lens directly above the left).

If the lenses are not polarized, you won't see any significant change in the brightness of reflections when rotating the frame. (If you need prescription sunglasses, you can modify this exercise by leaving your sunglasses on and slowly tilting your head to your right shoulder and then to your left. If your lenses are polarized, you will notice a significant reduction in reflections when your head is upright, versus when it is tilted to either shoulder.)

Are There Any Disadvantages of Polarized Lenses?

Polarized lenses usually provide better vision and comfort in bright sunlight than regular sunglasses. But there are some situations where they may be less than optimal.

For example, because polarized lenses reduce or eliminate glare from highly reflective flat surfaces, they can make icy patches on ski hills less visible. In these conditions, you may instead want to wear regular sunglasses to avoid a nasty fall. Just make sure that all sunglasses you wear when skiing block 100 percent of the sun's harmful UV rays, which are more intense at high altitudes.

Also, polarized lenses can reduce the visibility of images produced by liquid crystal displays (LCDs) found on the instrument panel of some cars, boats and planes, and on many ATM machines.



Article 2013, Access Media Group LLC. Source: Polarized Lenses and How They Work by AllAboutVision.com.

arthur
August 15th, 2013, 10:57 AM
You can also test your lenses with your computer LCD monitor. The monitor will become dark as you rotate your head if they are polarized. This is also how passive 3D TVs work. Odd lines and even lines have different polarization so your eyes see different images.

orca1946
August 15th, 2013, 12:57 PM
I had explain to my wife that her bike computer did not need a new battery --- turn your head 90 & voila !! now she can see it. Thanx for an in depth explanation on the effect.

JWAJack
August 15th, 2013, 06:18 PM
I've found that goggles with polarized lenses are helpful for open water swimming because of their effect on the reflected glare. The goggles I've used were from Finis and Zoggs (the latter being photo-chromatic as well).

nhc
August 16th, 2013, 05:28 PM
Like other high-quality sunglasses, polarized lenses also block 100 percent of the sun's harmful ultraviolet (UV) rays, and they are available in a variety of tints and materials.

Is this another way to make sunglasses with UV-protection or the only way?

arthur
August 16th, 2013, 06:50 PM
Is this another way to make sunglasses with UV-protection or the only way?
UV protection is not related to lenses being polarized. Making a lens polarized doesn't give it UV protection but any manufacturer bothering to make polarized lenses would also give them UV protection. Polarized 3D glasses don't have UV protection so they shouldn't be worn outside. Most sunglasses have UV protection and even clear glass can be made to have UV protection. I know about this a bit as I have UV and CPL (circular polarizer) filters for my SLR camera.

nhc
August 17th, 2013, 01:19 PM
UV protection is not related to lenses being polarized. Making a lens polarized doesn't give it UV protection but any manufacturer bothering to make polarized lenses would also give them UV protection. Polarized 3D glasses don't have UV protection so they shouldn't be worn outside. Most sunglasses have UV protection and even clear glass can be made to have UV protection. I know about this a bit as I have UV and CPL (circular polarizer) filters for my SLR camera.

So the above quote "Like other high-quality sunglasses, polarized lenses also block 100 percent of the sun's harmful ultraviolet (UV) rays" merely refers to the underlined part above in your reply? I once bought a pair of interchangeable sunglass lenses. On the package it has "Polarized" but does not say it has UV protection. When I asked the salesman, he said if it's polarized then it has UV protection.

arthur
August 19th, 2013, 11:12 AM
So the above quote "Like other high-quality sunglasses, polarized lenses also block 100 percent of the sun's harmful ultraviolet (UV) rays" merely refers to the underlined part above in your reply? I once bought a pair of interchangeable sunglass lenses. On the package it has "Polarized" but does not say it has UV protection. When I asked the salesman, he said if it's polarized then it has UV protection.Yes, polarized sunglasses use another layer to get UV protection. The polarization will block horizontally polarized photons, which includes visible light and UV, but will allow vertically polarized photons, including UV through. If your sunglasses were made by a reputable manufacturer, they will definitely have a UV layer.

nhc
June 11th, 2014, 03:06 AM
A while ago I was shopping for polarized sunglasses. To reassure me that the sunglasses he was showing me was polarized, the seller put the sunglasses over a white paper; through the sunglasses I could see a black picture (a drawing of a woman) on the white background. When he put a different pair of sunglasses over it, I couldn't see any picture, only a blank white. He said the latter was not polarized. How does it work? The picture must have some special feature?