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Polarised Sunglasses

Polarised Eyewear Lenses Explained

What are Polarised Lenses?

In sports and other outdoor leisure activities we react to what we see. We see because of the light that enters our eyes....no light = no vision. In bright sunlight, excess brightness and "glare" reduce our ability to see clearly and you end up "squinting" with watering eyes.

Glare results in a loss of visual performance, which is produced when an object or light source in the field-of-vision is brighter than the amount of light our eyes need to see clearly. Most tinted lenses will provide some absorption to reduce brightness, but only a polarised lens can effectively eliminate the glare.

So What Causes Glare?

Light is made up of waves travelling in different directions. Vertical light is useful to the human eye; it helps us see. Horizontal light, however, simply creates glare. Glare is concentrated light reflecting off a shiny surface, such as a car windscreen, white sand, pages of a book, water, snow or road surfaces. It reduces visibility and can make it uncomfortable, painful and even dangerous to carry on driving, cycling, skiing or just sunbathing.

How do polarised lenses compare to just tinted lenses?

Regular non-polarised sun lenses filter all light indiscriminately whether it is horizontal or vertical. Glare is dampened, but not eliminated. More importantly, by filtering all components of light, visual sharpness is reduced. Polarised lenses however, allow in the useful vertical light components which are preferred for clear vision, but eliminate the easily scattered and distorted horizontal light. Vertically aligned light allows the natural tendency of our vision to focus on the vertical component of an image.

Why are polarised sunglasses beneficial on water and in sport?

The glare of the sun on water surfaces is highly polarised. Indeed, the glare can be almost completely horizontally polarized, depending on the height of the sun which is why so often you are almost blinded by the light at sea and when fishing for example.

In addition, all reflections from objects above water are partially polarised. These include clouds and even the sky (the reflected sky gives most of its blue colour back to the sea).

Although the light from the sun is not polarised, it can be separated into two polarised components that are reflected and transmitted in different amounts by the surface of water. More of the horizontal light will be reflected than the vertical light thereby partially polarising the reflected light. Polarised sunglasses will stop the glare and make the sea appear more transparent enabling you to see fish and rocks below the surface for example and if playing Golf for example seeing your ball in flight

Are polarised sunglasses beneficial for driving?

Polarised sunglasses help when driving a car by reducing those bright reflections of the sun on the cars ahead. They tend to be horizontally polarised so ideal for vertically polarised sunglasses. The reason is that the surfaces that you see on the car in front of you (the back window, the rear door, and even the roof) is slanted towards you, while the sun will be more or less aligned in the vertical plane through both cars. Polarizing lenses will provide higher definition for driving, remove the dazzling effects and reduce fatigue. 

 

What are the advantages of polarised lenses?

A polarised lens offers the following advantages over non-polarised lenses: 

  • Improves visual comfort
  • Improves contrast and visual clarity
  • Reduces eye strain
  • Allows for a truer perception of colours
  • Reduces reflections and eliminates glare

When could polarised lenses pose a problem?

For certain sports or activities, polarized lenses are not the best choice. These are as follows:

  • Skiing in icy conditions. Patches of ice are easily identifiable as they reflect more light than snow. Wearing polarised lenses will make icy patches more difficult to see.
  • Spotting oil or icy patches on the road. For the same reasons above, we do not recommend using polarised lenses for riding motorbikes.
  • Viewing liquid crystal displays (LCDs) - Polarised lenses can make the liquid crystal displays of certain objects more difficult to read. 

How do I know if my sunglasses are polarized?

Just look through the glasses at the reflection of any object on a window panel. 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 polarised.  Another way is to hold them at 90° to another pair labelled as polarised and if the lenses go dark where the lenses overlap, then your sunglasses are polarized too. If there's no change, your lenses aren't polarized.  

Can you have clear polarising lenses?

No. Owing to the parallel row alignment of the iodine crystals in polarised lenses, if they were clear they would not block light in a specific direction.

Are all polarising lenses the same?

Not all polarised sunglasses block glare as well as they should. A polarising filter is no guarantee of an effective glare-blocking lens. It depends on the quality of the filter and how the lens has been produced. Polarised sunglasses usually cut out between 20% - 70% of reflected light but 100% of UV light.



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