The concept of polarizing light with man-made film was the idea of Edwin Land. Land would later become famous as the inventor of instant photography with his famous Land Polaroid Camera.
Land's original concept for his man-made polarizing film was to eliminate glare from auto headlights by placing polarizing filters over auto headlights and then incorporating a polarizing filter in car windshields.
His next (and better idea) was to incorporate his filter in sunglasses. American Optical was the largest optical manufacturer in the world at the time (1937) . Land invited their top people to a demo in a large Boston hotel.
Placing a fish tank in direct bright sunlight he asked the AO people to view the fish but all they saw was brilliant sunlight shining through the water. He handed them sheets of polarized film and asked them to look again. The fish became immediately visible.
The first Polarized Lenses were made from polarized sheet film laminated between two sheets of flat glass. The optics were questionable and delamination was a constant problem. In spite of this, these never-seen-before sunglasses soon became popular.
As plastic lenses grew in popularity, eventually laminated polarized lenses made in plastic were developed. Eventually plastic lenses became the most popular material for making polarized sunglasses. They were sold as over-the-counter drug store glasses and eventually became available in prescription form from eyecare professionals.
Today, all quality modern plastic polarized lenses are no longer laminated. A totally different technology is used in which an in-mold process has the film suspended in middle of the mold and the plastic monomer is poured around the film. As the plastic material solidifies around the film, the lens ends up as an integrated unit, making de-lamination of polarized lenses a thing of the past.
Polarized Lenses in Other Materials
Polycarbonate lenses are injection molded, a process that generates a great deal of heat. For this reason, polarized polycarbonate lenses use a different technology in which the polarizing film is applied to the front surface of the lens. Following application of film, the front surface is then covered with a tough scratch-resistant coating. As a result of this different structure, polarized polycarbonate lenses can be surfaced thinner than any other polarized plastics.
Polarized plastic lenses are also produced in various high index materials. This wide variety makes it possible to dispense polarized sun glasses for almost any prescription.
Principles of Polarization
Think of the polarized lens as a venetian blind with the venetian blind oriented so that light rays in the vertical meridian ( reflections coming from horizontal surfaces ) are blocked. The sunglass wearer's primary concern is with horizontal reflected glare. Horizontal glare comes from sunlight reflecting off the surface of water, roads, snow, car hoods, whatever.
One important fact is that polarized sun lenses must be properly oriented in the frame so that the lenses block the primary concern: horizontal reflected light ( as seen in this photo ). Fortunately, positioning of the lens is the lab or manufacturer's responsibility and not a concern of the dispenser.
By blocking horizontal glare, polarized lenses provide superior sun protection for a wide variety of activities and sports
Driving : polarized sunglasses benefits driving any kind of vehicle.
Fishing, boating or water sports : blocking glare from sunlight reflected from the surface of water is one of the more popular uses of polarized sunwear
FLYING-- airline pilots may notice stress patterns in the windshield of larger pressurized transport planes. For them, polarized sunglasses are not a viable option. This is seldom a problem with pilots of smaller private planes.
Outdoor sports :
Skiing is another example of a sport where polarized sunwear has become an essential accessory. Glare from snow can be blinding
Virtually any outdoor activity is more enjoyable with polarized sun lenses.
A phenomenon :
There is a noticeable visual phenomenon often associated with polarized lenses. It does not interfere with vision through the lenses but is created by a unique property of polarized light. The effect is called cross hatching . It can be seen in the side windows of automobiles as a cross hatch pattern in the glass. Auto side windows are tempered for safety reasons ( windshields are laminated ). Tempering induces stress that shows up in clear materials as a pattern when viewed through polarized lenses.
Why this happens:
This same principle of revealing stress with polarized lenses has been used in optical labs for years for revealing stress in mounted lenses. The famous AO Polariscope Instrument relies on two polarized lenses to reveal unwanted stress in rimless mountings or frames. The instruments is also used to verify that glass lenses have been heat-treated for impact resistance.
This instrument was produced by the American Optical Company who called their instrument "Colmascope". This useful instrument can still be found in use in many laboratories today.
Glasses are held between two polarized lenses with a light bulb shining through. If the least amount of strain or stress is present, it shows up immediately. This works with ophthalmic lenses in any material. It's the only sure way to avoid unwanted stress that can ultimately end in broken lenses.
Many modern instruments are often illuminated with LCD (liquid crystal diodes). When some of these are viewed through polarized sunwear, they can appear to be blacked out. This effect can be noticed in gas station pumps and some auto instrument panels.
Tilting the wearer's head to 45 degrees makes the numbers magically appear. This happens because the instrument makers did not orient the polarized lens in the instrument properly. Manufacturers are now aware of this and it is currently being corrected. It is not expected to be a problem in the future. With the growing popularity of polarized sunlenses, automobile manufacturers are being careful to properly align the orientation of their instruments
Color plays an important role in vision. For this reason, polarized lenses are available in a variety of colors.
AVAILABLE POLARIZED COLORS Glass: Gray A, C, Brown A, C, Yellow, Orange, Red, Violet, Blue, Green Polycarbonate: Gray C, Brown C 1.56 high index: Gray A, C, Brown A, C, Yellow, Orange, Red, Violet, Blue, Green, Melanin CR-39: Gray A, C, Brown A, C, Yellow, Orange, Red, Violet, Blue, Green, Melanin
Polarized lenses can now be ordered in a rainbow of colors, but which colors will work best for various lifestyle activities? Here are some suggestions to help you advise your sunwear patients.
Clear polarized lenses
Polarizing light is only possible when the film has some color. As a result, clear polarized lenses are not possible. The darker the color, the greater the polarizing effect. Most used colors are produced in two densities -- "A" ( lightest ) and "C" ( darkest ).
Gray transmits colors evenly and is the choice when color rendition is important. Gray A makes a good all-purpose sunglass. Gray A is good for overcast days. "A" shades of polarized lenses can be dyed darker to other colors or to a gradient, providing versatility for dispensers and wearers.
Gray is the color of choice for sunwear ( 65% usage in the United States ). Gray transmits all colors evenly. Gray is recommended for "blue water" fishing (ocean or deep lakes). Gray is recommended as a "all purpose" polarized lens.
This lighter shade of brown can be dyed darker to other colors or to a gradient. Brown A makes a good all-purpose sunglass. Brown A is good for overcast days. Brown A makes an excellent golf or ski lens for overcast days.
Brown provides improved contrast and depth perception. A good choice for shallow water fishing. Best choice for drivers who want sharpened contrast for "reading the road". Fashion authorities believe brown is a more flattering color on the face.
This color provides the maximum increase in contrast and filters out blue light. Frequently chosen by shooters for increased contrast in various shooting environments with improved marksmanship. Ideal for low light conditions such as driving on overcast or cloudy days
Red is a vibrant color that increases contrast. Often used for fishing in early morning or late evening hours. Used in target shooting for bright sunny conditions. For shooting applications, best with orange, green or black targets against a green or cluttered background. Also used for skiing and hunting.
Increases contrast and dampens certain backgrounds. Violet is often used by shooters in average or bright conditions. Fades out green backgrounds and enhances orange, green or black clay targets. Also used for skiing, snowmobiling.
Used in partly cloudy to sunny conditions. Used for tennis, golfing and snowmobiling. Blue is good for shooting green targets against a Desert background. Lets in maximum amount of blue light.
Slight contrast improvement over the Gray color. Maintains good color balance. Used for tennis, driving and golf, as well as an all-purpose lens color.
Golden brown color selectively blocks the highest amounts of violet and blue light ( termed high-energy visible light ). Blocking high-energy light is believed to reduce the risk of macular degeneration. Melanin provides high contrast with true color perception for golf and low vision. Recommended for sports, driving and everyday situations
More about Melanin :
Melanin is a naturally occurring substance in skin, hair and eyes that provides protection against harmful exposure to sunlight. Melanin is lost with age. Melanin lenses have synthetic melanin throughout the lens. It never loses its efficiency.
Polarized lenses are now available in a number of materials. Even high index is available in polarized form. It's now possible to provide polarized sunwear in any of these colors for virtually any patient
Polarized lenses are now available in each of the following materials:
1.56 high Index plastic
Dispensing Polarized Lenses
Why so are these sunlenses so popular?
Because polarized sunglasses are PERFORMANCE sunglasses
they do something:
They reduce light transmission
They reduce reflected glare
They increase contrast sensitivity
Polarized sunlenses offer 3 advantages:
#1 - Greater recognition: Eyewear consumers understand more about how polarized lenses work. They understand that polarized sunglasses are unique among sunwear.
#2 - Easy to demonstrate: Take two samples and cross one over the other or have patient look at shiny floor or magazine through polarized sunglasses or send them outside if the sun is out. Labs can also provide very effective polarized demonstration units.
#3 - Better price acceptance: Consumers understand that "performance" sunglasses provide greater value. There is always less price resistance to high-tech lenses.
Establish a routine
1. Display samples prominently: Establish highly visible area for a sunglass display.
2. Discuss sunwear with every patient: Even patients who require only reading glasses will appreciate a pair of quality plano sunglasses .
3. Feature polarized sunglasses: Lead off every sunwear discussion with a demonstration of polarized lenses.
A trade secret
Most top-of-the-line sunglasses in sporting goods stores have an AR coating on their back surface. People who try these on often comment on the noticeable added visual comfort they provide without knowing where it comes from. What they are responding to is the complete removal of backside reflections that are common to all dark sun lenses.
Establish a routine of recommending backside AR on all prescription polarized sunglasses.
Dispensing polarized sunwear requires no special skills. It does require understanding how polarized lenses work and . . . an ability to explain them properly to the patient.
The only other thing you will need is an adequate display of plano polarized samples