Polarization is like a chemical venetian blind which rearranges light and lets you see "through" glare. 100% Polarized lenses are the only truly effective way of eliminating glare. Water, fog, rain, snow or early morning dew, have reflective properties, which enhance reflected glare. In addition to water, glare is also a problem on roads and highways.
For years, boaters and fishermen have used polarized sunglasses to reduce glare from the water that they spend so much time on. In the past few years, however, the benefits of polarized sunglasses have been realized by a variety of other outdoor sports enthusiasts as well as by drivers and general use wearers. The popularity of polarized lenses has increased dramatically, as has availability.
Besides boaters, people that benefit most from polarized sunglasses include skiers, golfers, bikers, and joggers, who enjoy a clearer view and elimination of glare.
These sunglasses can be used for driving and in fact can reduce the glare that comes off a long, flat surface such as the hood of the car or the surface of a road. Polarized sunglasses can also be used indoors by light-sensitive people such as post-cataract surgery patients or by those exposed to bright light through windows.
How Do Polarized Lenses Work?
Light reflected from surfaces like a flat road or smooth water is generally horizontally polarized. This horizontally polarized light is blocked by the vertically oriented polarizers in the lenses.
The result: a reduction in annoying and sometimes dangerous glare.
There is some debate on the effects of polarized lenses on snow-covered surfaces. Some experts say they can reduce the intense glare that is caused by sunlight reflecting off snow. Others purport that the lenses are not satisfactory for sports such as downhill skiing because they may not provide the contrast the eye needs to distinguish ice patches or moguls.
In addition, polarized lenses may also react adversely with liquid crystal displays (LCDs) found on the dashboards of some cars or in other places such as the digital screens on automatic teller (bank) machines. The problem with LCDs is that when viewed through polarized lenses from a certain angle, they can be invisible.
However, for most other sports and activities, polarized sunglasses can offer great advantages. And today, many types of polarized lenses are available on the market.
Polarized progressive lenses are perfect for the presbyope who is also an outdoor sports aficionado. And polarized photochromic lenses, which change from dark outside to light inside, are right for the light-sensitive person who changes environments frequently (inside to outside and vice versa).
Whether you spend your time boating or waterskiing, in-line skating or mountain biking, driving or jogging, polarized sunglasses are an excellent choice.
Why (fisher)men prefer them polarized?
Because they are more FUN when the SUN is up !!!
Fact: The glare of the sun on the sea (and other surfaces) is highly polarized !
Indeed, the glare can be almost completely horizontally polarized, depending on the height of the sun. In addition, all reflections from objects above water are partially polarized. With polarized sunglasses the sea appears more transparent! The image to the left was taken through a polarizer with its transmission axis oriented horizontally. The image to the right was taken through a vertical polarizer. Which one would you like to use for fishing?
Surf through horizontal polarizing filter
Surf through vertical polarizing filter
This is just one more example of polarization by reflection. Although the light from the sun is not polarized, it can be separated into two polarized components that are reflected and transmitted in different amounts by the surface of the water (Fresnel laws). More of the horizontal component will be reflected than the vertical component, thus partially polarizing the reflected light (except if you look at a glancing angle or straight down).
The polarized sunglasses used by fishermen have polarized filters with the transmission axis oriented vertically to block the light reflected by the water surface. Note that if the fisherman moves his head up or down (nodding) the line joining the temples remains horizontal and the sunglasses continue to block the glare (of course, if he leans his head to one side the filters start to point in the wrong direction). By the way, they are not only used by fishermen but in all other water-sports. They are also becoming popular with truck drivers and for general outdoor activities. The last five years have seen a jump in their sales and are the fastest growing segment in eyewear.
Frequently asked questions about polarized sunglasses
How do I know if mine are polarized?
Very easily done. Just look through the glasses at the reflection of any object on a window panel (but not at yourself! you have to look at an angle to the glass). Then, turn the sunglasses around as if they were the hands of a clock facing you. If the intensity of the reflection doesn't change with respect to what you see through the window, they are not polarized.
I still don't understand, why are polarized sunglasses better than normal dark sunglasses?
Normal sunglasses decrease the intensity of everything by the same amount. Polarized sunglasses can selectively eliminate the reflection from light coming from above the water surface.
Then, could polarized glasses be crystal clear?
Nope, they will always decrease the intensity of unpolarized light by at least half. In practice somewhat more because of losses in the material. They come in all shades from light gray (only polarizing) to very dark (polarizing plus black tint), and also light sensitive (photochromatic). You can even find sunglasses with darkness adjustable by the user.
Do polarized sunglasses help see fish and rocks below the water surface?
Yes. First, if there is glare, they help a lot by reducing its blinding effect. Second, even without glare they selectively reduce other reflections from objects above water, including clouds and even the sky (the reflected sky gives most of its blue color to the sea). Finally, light coming from under water is slightly polarized in the vertical plane (polarized on transmission). The end effect is that the water seems darker but more transparent! But remember, it only works if you look at the water at some angle and not straight down.
Does it matter the time of the day?
Yes. Maximum polarization is obtained when the sun is at about 37 degrees from the horizon (in theory 100% polarization at the Brewster angle). If the sun is very low or very high the sunglasses will be of little help in filtering the glare in calm seas. A rule of thumb would be that polarized filters limit the glare from calm waters for a sun altitude between 30 and 60 degrees (but see next question). Anyway, it should be stressed that polarization won't help in looking directly at the sun (except in decreasing the overall intensity of everything by half).
Does it matter the choppiness of the sea?
Yes. When the sea is ruffled the sun reflection becomes the familiar glitter, an elongated pattern of shimmering water stretching towards the sun. Because different parts of the glitter are reflected from different wave slopes, the degree of polarization varies from place to place. In those conditions the sunglasses will also help for high or low suns and the benefit will depend on where you are looking. As a side note, the width and length of the glitter together with the altitude of the sun can be used to compute the height of the waves without ever getting close to them!
Can polarized sunglasses help when driving a car?
Yes. Those pesky bright reflections of the sun on the cars ahead can sometimes be attenuated a good deal. They tend to be horizontally polarized, thus perfect for vertically polarized sunglasses. The reason is that the surfaces that you see on the car in front of you (the back window, the trunk door, and even the roof) will be slanted towards you, while the sun will be more or less aligned in the vertical plane through both cars (if not you wouldn't see its reflection from those surfaces). However, if the sun is relatively low behind you, the sun rays will be near perpendicular to the reflecting (vertical) surfaces which won't polarize the light. The sunglasses will help more with the reflections from the glass than from the metal as the former are polarized to a higher degree. What about the brightness of the road itself? That light is also partially polarized, but by scattering (as opposed to reflection). The direction of polarization will change with the direction of the road with respect to the position of the sun. The rule is that the polarization is tangential to a circle centered on the sun. That means that if the sun is in front, behind, or high above, the road brightness will tend to be horizontally polarized and the filter of the sunglasses will provide some help. However, if the sun is to one side, the polarization will rotate vertically, the more so the lower the sun happens to be. Of course, if the road is wet you get the same anti-glare power than at sea.
Can polarized sunglasses help in skiing and other non-water sports?
Sometimes yes, sometimes no. The snow glare is not polarized, so they won't provide extra help in that regard (although often advertised for that purpose). But, with the sun high, the air-light (haze + sky) near the horizon is polarized by scattering and the polarized sunglasses can make features far away really stand out (this is used in fire detection). On the other hand, with the sun low the sunglasses could be detrimental looking south or north, as the air-light would be vertically polarized. Other situations can be thought were they would be useful, but remember that one reason they are so good in water sports is that the reflector always remains horizontal!
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February 3, 2008
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