Many manufacturers of high quality sunglasses boast of their polarized lenses, but they rarely explain what that means or how the benefits of polarized sunglasses are achieved.
How Polarization Works
Light moves as a wave, just like waves of water on the surface of the ocean. Water waves, however, are usually all oriented vertically; while they might travel in different directions, the oscillation (or vibration) is always vertical. Water waves naturally have one polarization.
Light waves, on the other hand, do not. As explained in The Physics Classroom, even if they are moving in the same direction, light waves oscillate in all directions and are unpolarized. A beam of light traveling parallel to the ground can vibrate horizontally, vertically, or at any of the diagonal angles in between. When light hits a surface like glass, water, or snow, the surface reflects more light that is horizontally polarized.
A polarizing lens filters out light that is vibrating in a certain direction. For sunglasses, that direction is horizontal, in order to filter out glare from reflective surfaces. Polarized sunglasses actually filter out a whole wide range of polarizations and only let light through that is vertically (or close to vertically) polarized.
The Benefits of Polarized Sunglasses
Polarized lenses are great for reducing glare—light reflected off snow, water, or other shiny surfaces—according to the Mayo Clinic. This makes them ideal for snow sports like skiing and water sports like fishing or canoeing. They are also useful for driving, as they are particularly effective at reducing glare on wet roads.
Do Polarized Lenses Offer UV Protection?
The most important factor in choosing sunglasses is UV protection (aside from looking awesome, perhaps). The National Eye Institute recommends lenses that block 99 to 100 percent of UVA and UVB rays. Polarization and UV blocking are mostly unrelated—polarized lenses can be, but are not necessarily, UV blocking. So even when buying glasses with polarized lenses, make sure to also check for the UV rating.
The Disadvantages of Polarization
While polarization mostly makes vision clearer, it can interact strangely with certain light sources. One thing people tend to notice is that if you look at the sky on the horizon and tilt your head to the side, the sky changes color; however, this is not usually a major problem.
What can be annoying, however, is when the polarization interacts with screens of electronic devices or treated glass. Certain car windshields will create distinctive patterns when viewed through polarized lenses. This is because windshields are made from tempered safety glass, which is treated to break into small, round granules rather than dangerously sharp pieces.
LCD screens and certain other electronic devices can have a similar interaction, creating swirling color patterns that obscure the screen. To make sure this won’t be a problem for you, borrow a pair of polarized sunglasses and try looking through your car windshield and at any electronic devices that you like to use while outside.
For questions or comments, contact Woodhams Eye Clinic.
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