Polarized Sunglasses

What is Polarization?

When light strikes a surface, it becomes polarized, which means that the photons in the light are all vibrating in one direction, instead of in random directions. The light waves travel from "pole" to "pole" along that plane. This phenomenon is what causes the glare reflected from a car window or chrome, or from a wet pavement. This glare distorts the true color of objects and makes them harder to distinguish. It also causes a mirror-effect on wet surfaces, so that objects below the water's surface cannot be clearly distinguished.

What Does a Polarized Lens Do?

Polarized lenses filter the waves of light by absorbing some of the reflected glare while allowing other light waves to pass through them. The most common illustration of how a polarized lens works to reduce glare is to think of the lens as a Venetian blind. These blinds block light that strikes them from certain angles, while allowing light from other angles to pass through. A polarizing lens works when it is positioned at a 90-degree angle to the source of the glare. Polarized sunglasses, which are designed to filter horizontal light, are mounted vertically in the frame, and must be carefully aligned so that they will properly filter the light-waves.

What are Polarized Sunglasses Made of?

The first polarized lenses were made of a polarizing film that was sandwiched between two flat sheets of glass. Because glass lenses are so heavy, however, the advent of plastic and polycarbonate materials, which are lighter and thinner, made the glass lenses less popular.

One of the problems with early polarized sunglasses was delamination, when the polarizing film separated from the pieces of glass or plastic. This problem has been solved with modern lenses, as the plastic can be melted and poured into a mold in which the polarizing film has been suspended. The plastic then hardens around the film, creating a solid material, rather than a layered one.

Polycarbonate lenses are created in a different manner, since polycarbonate lenses are injection molded and the heat from the process would destroy the polarizing film. For polycarbonate lenses, the polarizing film is applied to the front of the lens and covered with a scratch-resistant coating. This process means that polarized polycarbonate lenses are the thinnest and lightest polarized lenses available.

What Colors are Available?

All polarized lenses have some color, as it is possible to polarize light only when the film is colored. Darker colors provide higher levels of polarization.

Depending on the material from which the lenses are made, a variety of colors is available in polarized lenses. However, the color can help filter light in other ways which may be helpful or distracting, depending on the activity in which the sunglasses will be worn. The following colors are available in each of the following lens materials:

• Glass: light or dark gray, classic gray, light or dark brown, red, orange, yellow, green, blue, violet, copper.
• CR-39 (a plastic polymer -- allyl diglycol carbonate): light or dark gray, classic gray, light or dark brown, red, orange, yellow, green, blue, violet, copper, melanin.
• Plastic 1.56: light or dark gray, classic gray, light or dark brown, red, orange, yellow, green, blue, violet, copper, melanin.
• Polycarbonate: dark gray, dark brown.
• High-Index Plastic 1.60: light or dark gray, light or dark brown.

How Do I Choose the Right Color?

It is important to choose the right color lens for the activity in which you will be wearing the sunglasses. Each color affects vision in different ways.

• Gray: The most popular color for sunglasses in the U.S., gray transmits all colors evenly. It makes a good everyday or all-purpose choice of sunglasses. It is recommended for ocean fishing, where the water tends to be blue. "Classic gray" is a color that provides near-natural vision and true color perception.
• Brown: Because brown improves contrast and depth perception, it is best for driving and shallow-water fishing. Light brown is a good color for overcast days and is recommended for skiers and golfers. Brown is another popular color, especially among the fashion-conscious, because many fashion authorities believe that brown is flattering to the face.
• Red: Red is primarily used by sportsmen working in bright, sunny places.
• Orange:Like yellow, orange lenses filter out blue light and increase contrast sensitivity. Orange is a popular color among skeet shooters because it makes the targets more visible.
• Yellow: This color filters out blue light. Because it provides the highest level of contrast, it is perfect for cloudy-day driving and for marksmanship practise.
• Green: Green improves contrast slightly, and keeps a good balance among the colors of light. It is a popular color for tennis, golf, or driving.
• Blue: Blue allows the most blue light to filter through, so it is good in partly cloudy weather. Blue is a popular lens color among tennis players and golfers.
• Violet: Violet causes green to fade and enhances orange, green, and black. It is good for shooting under average conditions.
• Copper: Copper provides maximum contrast and is best for any activity in which good vision is important.
• Melanin: Melanin lenses are relatively new on the market. They are a golden-brown tint and provide high contrast. Melanin lenses are believed to help protect against macular degeneration. Melanin is a pigment that occurs naturally in the body and protects the body from harmful exposure to sunlight. Melanin lenses are made with a synthetic form of this pigment that never loses its potency.

Cautions and Recommendations

• Most opticians recommend an anti-reflective coating on the inside of the polarized lens.
• The time of day matters when you are using polarized sun glasses. If the sun is very low or very high, the sunglasses will not filter the glare as well, because the best polarization is obtained when the sun is 37 degrees from the horizon.
• Polarized lenses can hinder your ability to read an LCD screen. If you find that an instrument display appears black when you look at it through your polarized sunglasses, tilt your head at a 45 degree angle to the screen and the screen should become readable.
• Some polarized sunglasses, especially 3-D polarized glasses, can cause severe vertigo because the filters for these glasses are oriented somewhat differently than those for regular polarized glasses.
• Polarized lenses can create an effect called cross-hatching that makes car windows (made of tempered glass) appear to have a pattern of lines, splotches, or large dots in the glass. This is due to the stresses created in tempered glass by the tempering process. These stresses are revealed when the light filters through the polarized lens.

Who Makes Polarized Sun Glasses?

Most reputable, high-end designers have a line of sunglasses. Some of the more popular brands include Acies, Anarchy, Bolle, Kaenon, Maui Jim, Oakley, Ray-Ban, Serengeti, and Spy.

Related Sunglasses Links

• Choosing Sunglasses
• UV Index
• Prescription Sunglasses
• Ray-Ban Sunglasses
• Anarchy Sunglasses
• Spy Sunglasses
• Maui Jim Sunglasses