Light rays travel in all directions radiating out from the source of the light in question. However, when sunlight strikes a flat surface such as the surface of a lake, a road, a sandy beach or a snow field the light is reflected and this light is said to be partially polarized.
In essence, as you sit in a boat fishing for example with light entering your eyes from all around you, you will also experience an additional source of reflected light entering the eyes in a series of horizontal bands from wherever you are looking on the surface of the water.
Way back in 1929 Edwin Land, who was then a freshman at Harvard University, was studying this particular problem and produced a thin transparent sheet, then called a J sheet and later renamed as Polaroid, which was embedded with tiny crystals and which could filter out this source of reflected light. Later, in 1937, Land founded the Polaroid Corporation in Boston and the technology of providing polarized filters spread widely to everything from car headlights to camera lenses and anti-glare computer screens.
One of the earliest uses of polarization was however to be seen in sunglasses following a fishing trip by one of Land's colleagues. The colleague took a scrap of Polaroid with him on his fishing trip and returned with a large trout which he had caught because the Polaroid sheet had reduced the glare on the stream and allowed him to see the fish. Not long afterwards the first Polaroid sunglasses were produced and sales were brisk in sporting shops across America.
The use of Polaroid in reducing glare was clear and today the technology is widely used in the manufacture of sunglasses. Like everything else however there are also a lot of cheap sunglasses sold that claim to be polarized but which are not. So, how do you tell if your glasses are indeed polarized?
Well, you can't tell by simply looking at them because the polarizing film is a thin clear sheet embedded in the lens and outwardly polarized sunglasses look exactly the same as ordinary sunglasses.
The first thing you need to do is to find a flat surface that is reflecting light and then hold the glasses a few inches in front of your face so that you are viewing the surface through one of the lenses. At this point the reflection from the surface should be significantly reduced.
Next, turn your sunglasses through ninety degrees. At this point the polarizing filter which was originally at right angles to the reflected light and blocking its passage through the lens will now be aligned with it so that much more of the reflected light should pass through the lens making the surface appear much brighter.
If there is no significant difference when viewing the surface with your sunglasses held in their normal position and turned through ninety degrees then your sunglasses are not polarized.
Polarized sunglasses have a variety of uses and are particularly useful for activities such as fishing, boating, skiing and driving. There are however some circumstances in which polarized glasses may well be more of a hindrance than a help.
In icy conditions, for example, skiers will often see, and therefore be able to avoid, patches of ice because ice will reflect more light than snow and thus stand out. Wearing polarized sunglasses will reduce this glare and thus blur the distinction between snow and ice.
Similarly many car windshields today are themselves partially polarized and wearing polarized sunglasses may create an interference pattern on the windshield reducing your visibility.
Polaroid and the technology of polarization have done much to add to the effectiveness of sunglasses and, as long as you are aware of both its uses and dangers, it will allow you to wear your sunglasses with both comfort and safety.
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