Polarised Sunglasses - Is there any difference?

Mark Rodgers: A question I am often asked in the shop is what are the benefits if any, of purchasing a good pair of polarized sunglasses over a cheap pair? There are big differences between sunglasses from different lens tints to quite sophisticated lens compositions and technologies. A good pair of polarised sunglasses should provide protection from ultraviolet (UV) rays in sunlight. UV light can damage the Lens, Cornea and Retina in the eye. Good sunglasses can eliminate UV rays completely. Sunglasses provide protection from intense light. When the eye receives too much light, it naturally closes the iris. Once it has closed the iris as far as it can, the next step is squinting. If there is still too much light, the result is damage to the retina. Good sunglasses can keep light at a safe level. Polarised sunglasses provide protection from glare or reflected light using a filter. Different colour tints of lenses eliminate specific frequencies of light. Certain frequencies of light can blur vision and others can enhance contrast. Choosing the right colour for your sunglasses lets them work better in different situations.

When you purchase a cheap pair of sunglasses, you may give up some of these qualities and can potentially make eye damage worse! If your sunnies have little or no UV protection the light that is blocked causes your iris to open. This allows more harmful UV light in, that can damage the lens and retina. Cataracts are the result of gradually accumulating damage to the proteins of the lens. The most important source of this damage is exposure to ultraviolet (UV) radiation. Retinal diseases is one of the leading causes of blindness. Macular degeneration, the accumulation of damage in the retina, is the leading cause of blindness from retinal disease. Slowly, over the years, the macula is irreversibly damaged by exposure to UV radiation. About one third of adults over age 65 experience this steady decline of central vision, not correctable by glasses.

This diagram shows how a good pair of polarised glasses should work. The percentage of available light allowed to reach the eye can vary. Different tints offer specific VLT(Visual Light Transmission) to enhance vision in various light conditions.

There are three main lens types that are used. The very cheapest sunglass lenses are made from plastic and usually contain optical distortion. Polycarbonate lenses are a strengthened synthetic plastic that is very light. Glass lenses offer the most scratch resistance. Better quality sunglasses generally use much superior materials for the frames which make them  lightweight, strong and flexible. Other features may include anti slip nose and ear pads.
Higher quality sunglasses use a greater variety of technologies to eliminate the problems with light. Here are some explanations of what these do.

Anti reflective coating - This is a very hard thin film that is layered on the lens. This reduces the light that hits the back of the lens and reflects back into our eyes. A well fitted wrap around style lens will also reduce the amount of light that gets in behind. Scratch resistant coating – Glass is naturally scratch resistant but polycarbonate lenses often have these extremely hard and thin coatings added to the lenses.

Tinting – The colour of a lense tint determines the parts of the light spectrum that gets absorbed by the lenses. Amber, brown and copper tints all absorb higher frequency colours such as blue. Although the natural colours of objects appear different contrast and clarity is improved. That is why theses tints are most popular for fishing.

UV coating - A good UV coating on your sunglasses can eliminate UV radiation, and you should check to make sure that your sunglasses filter out 100 percent of UV rays.

Photochromic Lenses (Photochromatic) – These are lenses that darken when exposed to sunlight. They have substances in them that when exposed to UV rays  these molecules undergo a chemical process and change shape. The new molecular structure absorbs portions of the visible light, causing the lenses to darken. The intensity of the UV light from the sun determines how many of these molecules change shape.

Most of the glare that causes you to wear sunglasses comes from horizontal surfaces, such as water. When light strikes a surface, the reflected waves are polarised to match the angle of that surface. A highly reflective horizontal surface, such as a lake, will produce a lot of horizontally polarised light. Therefore, the polarised lenses in sunglasses are fixed at an angle that only allows vertically polarised light to enter. Polarised  filters  are most commonly made of a chemical film applied to a plastic or glass lens surface. The chemical compound used consists of  molecules that naturally align parallel to one another. When applied uniformly to the lens, the molecules create a microscopic filter that absorbs any light matching their alignment.

There is now a huge range of different shapes and styles to suit everyone’s size and  tastes. Some have interchangeable lenses you can change depending on whether it’s overcast or sunny. So the answer to the question "is there any difference between polarized glasses?" is undoubtedly yes.

If you have any questions about glasses feel free to give me a call, I am happy to help at any time, click here for our shop contact details: Fishermans Loft Website

Author of this article: FishermansLoft(1)