The POWER Of Polarization
The development of polarizing filters and how polarized sunwear benefits consumers
Jenean Carlton BA, ABOC, NCLC
Polarized lenses offer patients advantages that tinted lenses simply cannot. Absorptive tints cut down on brightness by reducing the overall amount of light transmitted through a lens, but only polarized sunwear eliminates reflected glare for sharper, safer, and more comfortable vision when driving or enjoying outdoor activities.
Reflected glare is common in the outdoors on water, roads, snow, windshields, and other flat, reflective surfaces. Glare can be bothersome, discomforting, or even so bright as to temporarily “blind” individuals and create unsafe conditions.
Drivers squint to try to see clearly, often turning their gaze away from the road when faced with intense glare. Glare turns everyday driving conditions—such as pedestrians walking across the street or cars stopping abruptly—into potential hazards that could be avoided by wearing polarized sunwear.
In addition to how these advanced lenses benefit consumers, this in-depth look at polarization explores how the lenses were developed as well as the current methods used in fabricating polarized sunwear.
EARLY FASCINATION LEADS TO INVENTION
Edwin Herbert Land (1909-1991) was born in Connecticut, and from an early age was interested in the properties of light. As a young boy, he enjoyed playing with kaleidoscopes and stereoscopes—toys that heightened his curiosity with light and color.
At 13, Land attended a science camp for boys and marveled as he watched one of the camp leaders use a piece of Iceland spar (a transparent type of calcite) to demonstrate the effects of polarization by eliminating glare on a table top. During this same trip, Land was driving an automobile one evening and nearly collided with a wagon. He thought that automobile headlights should be stronger, but wondered how they could be prevented from blinding the drivers of oncoming vehicles. Land and his friends discussed how glare might be controlled by developing polarized headlights.
By the time he was 17, Land was experimenting with polarization. One day, while working with a set of tourmaline crystals (a semi-precious gem stone), he noticed that as he rotated the crystals in his hands, light passing through them changed from dark to bright, depending on the crystals’ orientation. He concluded that light passing through the tourmaline crystals changed color because the gem stones acted as a dichroic material—dichroism being the property of some crystals to exhibit tourmaline crystals.
He noticed that as he rotated them, light passing through changed from dark to bright, depending on their orientation. Based on this, Land wondered if it was possible to create large sheets of polarizing filters using tourmaline. Unfortunately, tourmaline was difficult to obtain and only available in small quantities.
Never one to give up on a challenge, Land began to ponder ways to develop polarizing filters without the use of tourmaline crystals. While contemplating materials that could possibly have the same polarizing properties of tourmaline, his thoughts took him back to his favorite childhood toy—kaleidoscopes.
The kaleidoscope had been invented about a century earlier, in 1816, by British physicist Sir David Brewster. To create the eyepiece, Brewster used herapathite crystals, a crystalline form of iodoquinine sulfate, which functioned as polarizers. After studying Brewster’s work, Land wondered if herapathite crystals could be useful in developing sheets of polarizing films.
Land entered Harvard University in 1926 but, driven to continue his work on polarization, he dropped out his freshman year. He continued his research on herapathite crystals, but determined that they were extremely thin and fragile, and that they polarized light in multiple directions, which resulted in a useless array of light.
He then modified his experiments by making the herapathite crystals much smaller than in earlier trials. The result? If aligned properly, the smaller crystals would collectively polarize light much like the larger tourmaline crystals.
| USING LCD SCREENS |
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TVs, tablets, computer screens, ATMs, smartphones, and gas pumps all use LCD screens. This causes problems for polarized lens wearers because LCD screens are also polarized. Because the LCD output is polarized, the image can be lost if it is polarized in a plane that the glasses block. If an LCD’s polarization is oriented in the same way as that of the glasses, there’s no problem. Gas pumps can be difficult to read while wearing polarized lenses because the polarizing filter on these screens is oriented at a position that is perpendicular to the filter of the eyewear. Users of computer tablets may notice that viewing their devices in the vertical (portrait mode) while wearing polarized sunwear effectively blackens the screen. That’s because the polarizing filter in the LCD is oriented perpendicular to the filter in the eyewear, effectively blocking the image. To solve this, users can turn the tablet horizontally and use it in landscape mode. This way the polarizers aren’t perpendicular to each other and will not block light emitted from the device. |
His experiment with smaller iodoquinine sulfate crystals was a success. In 1928, Land created the first sheets of polarizing film. With patents applied for, he returned to Harvard in 1929 and presented a lecture on the development of his polarizing film. The university was so impressed that they provided him a laboratory so he could continue his work with polarization.
Instead of staying to finish his degree, however, Land endeavored to manufacture and commercialize his polarizing film. And, in 1933, he partnered with George Wheelwright, one of his physics professors, to form Land-Wheelwright Laboratories in Boston.
| DRIVING AND POLARIZED LENSES |
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Drivers wearing polarized lenses often view light or dark spots in a grid-like pattern on side and rear automobile windows. There are many thoughts as to why this phenomenon occurs, with one theory being that the heat-tempering process, necessary to make glass stronger in automobile windows and even some windows in buildings, creates stress within the glass. It is thought that the stress in the glass causes birefringence, which is the double refraction of light in a transparent material. The effect of birefringence is that unpolarized light is separated into two polarized beams of light with perpendicular directions of vibration. It is thought that the spots or grid patterns are seen on car windows when wearing polarized eyewear are because portions of the light transmitting through the windows is polarized in a plane that is perpendicular to the direction of the polarizing film in lenses. Car manufacturers do not polarize the glass in windshields for safety reasons. If the front windshield were polarized, drivers wearing polarized lenses could turn their head in just the right way to suddenly block incoming light. |
Two years later, in 1935, American Optical signed a licensing agreement to use polarizing film from Land-Wheelwright Laboratories for the production of sunglasses. In 1937, the Land-Wheelwright Company was reorganized to become the Polaroid Corporation.
After World War II began, Land’s invention took on new importance as polarized filters were used in military-issue sunglasses as well as in the development of other military devices such as dark-developing goggles, target finders, and the Vectrograph—a stereoscopic system used to locate the positions of camouflaged enemy soldiers. A Vectrograph used in the optical industry is the Titmus Fly Stereotest.
Though the war made Land’s polarizing filter widely popular, it jeopardized the fabrication because of a shortage of the drug quinine, which was needed to create iodoquinine sulfate, the tiny crystals used to produce Land’s polarizing filter. Quinine was in short supply, though, because it was necessary to treat soldiers with malaria.
Faced with the shortage, Land endeavored to develop a new polarizer that wasn’t based on the use of microcrystals. The result was a new polarizing film consisting of clear plastic sheets of polyvinyl alcohol (PVA) that were heated and stretched in a given direction to many times its original length. The PVA sheets were dipped in iodine, which absorbed into the molecular chains forming parallel, darkened lines that polarize light. The film was then laminated to a solid sheet of plastic, such as cellulose acetate butyrate (CAB), for stability. Not only did Land’s new invention work, it worked better than his original polarizing film made with iodoquinine sulfate. In fact, the majority of polarized lenses created today still use a PVA polarizing film.
POLARIZATION DEFINED
How does polarization work? Waves of light consist of an electrical and magnetic field and are randomly oriented, where the electrical field of a wave may vibrate in any direction perpendicular to the direction of the wave motion. This is unpolarized light, meaning that electromagnetic waves are vibrating in all directions. Though unpolarized light is difficult to visualize, think of it as a wave with half of its vibrations in a horizontal plane and the other half in a vertical one.
A polarizing filter has specially aligned elongated molecules that allow the passage of light rays traveling in one orientation; light traveling in other orientations is blocked. By definition, a ray of light is polarized if the vibrations of its component waves are confined to one direction. Polarized sunwear lenses, for example, eliminate glare because they block horizontally reflected light waves.
A polarized lens works when it is positioned at a 90-degree angle to the source of the glare. Polarized lenses are designed to filter horizontal light and are mounted in a vertical position in frames. For the filter to work properly it must be correctly aligned so that it will block the horizontal waves. As a result, polarizing filters in lenses include alignment markings to assist the laboratory in mounting them.
Lenses that offer a constant level of polarization have the polarizing film laminated between two pieces of lens material. This creates a composite lens consisting of three layers. Other manufacturers embed the polarizing film in the mold during production to encapsulate the film within the lens material. This process reduces the chance of delamination, which was a concern with early polarized designs.
| LAND’S INVENTIONS |
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Physicist and inventor Edwin H. Land developed the first modern polarizing film. Its most popular use was for instant cameras, film, optical lenses, 3D glasses, and LCD displays. His Polaroid Land camera was the first commercially successful self-developing camera. He received more than 500 patents for his innovations in light and plastics. Polaroid image from Safilo. 
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One popular method of fabricating polarized polycarbonate lenses is to first create a thin polarized “disc.” This is accomplished by encapsulating a polarized film between two thin layers of polycarbonate material. The disc is inserted into the mold cavity, and the remaining polycarbonate lens material is injection-molded onto the disc to form the lens blank.
| TESTING FOR POLARIZATION |
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One way to determine if lenses are polarized is to hold one of the lenses in front of the other and turn them slowly. If the lenses darken and then lighten again while rotating them they are polarized. When the polarizing filters are perpendicular to each other, the majority of the light traveling through the lenses is blocked. This phenomenon will not occur with non-polarized lenses. Polaroid image courtesy of Safilo. |
THE NEXT DEVELOPMENT
Vantage lenses from Transitions Optical are different from lenses that offer a constant level of polarization. These lenses are clear and non-polarized until exposed to UV, at which point the photochromic dye compounds darken and align in such a way as to result in a variable polarized lens.
In general, polarized lenses are far superior to non-polarized lenses for outdoor daytime use, but there are situations in which they can cause concern for patients, such as when using a device that has a liquid crystal display, known as an LCD screen (see sidebar).
However, because of the superiority of polarized lenses for the majority of time spent outdoors, more and more consumers are enjoying their myriad benefits.
By blocking the ‘visual noise’ of reflected glare, polarized lenses offer clearer, safer, more comfortable vision than absorptive tinted lenses. EB
Understanding Polarized Filters
This puzzle pertains to the development of polarizing filters and how polarized sunwear benefits wearers.
across
1 The majority of polarized lenses today still use a ______ polarizing film.
5 In 1928, Land created the first sheets of ______ film.
8 A property of some crystals to exhibit different colors, primarily two different colors, when viewed along different axes.
10 Herapathite crystals are a ______ form of iodoquinine sulfate.
13 Edwin ______ was interested in the properties of light from an early age.
14 In 1935, ______ ______ signed a licensing agreement to use Land’s polarizing film for the production of sunglasses. (Two words)
15 Brewster used ______ crystals, which functioned as polarizers, to create the eyepiece for his invention.
17 ______ crystals act as a dichroic material.
19 The PVA sheets were then ______ to a solid sheet of plastic for stability.
21 ______ sunwear eliminates glare.
22 ______ screens are polarized.
23 Reflected ______ is common in the outdoors.
down
1 When two polarizer filters are ______ to each other, the light passing through is blocked.
2 Land’s new polarizing film consisted of clear plastic sheets of ______. (Two words)
3 Rays of light consist of an electrical and ______ field.
4 The ______ was invented by physicist Sir David Brewster in 1816.
6 ______ is the double refraction of light in a transparent material.
7 Land’s experiment with smaller ______ sulfate crystals worked.
9 Polarized sunwear eliminates glare by blocking ______ reflected light waves.
11 Herapathite crystals were extremely fragile and ______ light in multiple directions.
12 A common ______ used in the optical industry is the Titmus Fly Stereotest.
16 ______ was in short supply during the war as the drug was used to treat soldiers with malaria.
17 Glass used in side and rear vehicle windows is heat ______.
18 Normal light waves are ______ oriented.
20 ______ absorbed into the molecular chains forming parallel, darkened lines that polarize light.
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