Specs Appeal: How Polarised Sunglasses Work

By John Smith, Published February 12, 2014

How Polarised Sunglasses Work

Visible light is made up of horizontal and vertical light rays. Ordinary sunglass lenses work by reducing the amount of light transmitted through them by tinting. Polarised sunglasses, on the other hand, filter out all the horizontal rays, including those reflected off horizontal surfaces such as wet roads and water.

Unlike conventional sunglasses, polarised sunglasses don’t just dim down the rays they cut them out completely. They’ve been around for years too, and have been the sunglasses of choice for fishermen and boaters who need to block the glare reflected from the surrounding water.

But the attraction and benefits of polarised sunglasses are catching on, especially with people who spend a lot of time outdoors and need to eliminate unnecessary glare, including joggers, skiers, golfers and cyclists. They’re also good for wearing whilst driving and are effective at reducing glare from the road’s surface.

For people who are particularly sensitive to the light, polarised sunglasses can be worn indoors, especially for people recovering from cataract surgery and people who are continually exposed to bright light through windows.

What causes glare?

What causes glare for sunglasses?

Light is made up of waves all travelling in different directions. It’s made up of vertical light which is useful to the human eye, and horizontal light which just creates glare.

Glare is concentrated light reflecting off a shiny, horizontal surface such as snow, water or a car windscreen, and reduces visibility to the extent of being uncomfortable, painful or dangerous to drive, ski or cycle.

How do polarised lenses work?

Light reflected from surfaces such as smooth water or a flat road is generally horizontally polarised, meaning that rather than light being disseminated in all directions reflected light usually travels in a more horizontal direction. The result of this is an irritating, occasionally dangerous light intensity we more commonly call glare.

Polarised sunglasses have a special filter that blocks out this glare so you can see better and your eyes are more comfortable. There are some exceptions to the rule though for example, downhill skiing, when seeing glare shining off icy patches will actually help you spot potentially hazardous areas.

Why are polarised sunglasses beneficial for driving?

why are polarized sunglasses good for driving?

Polarised sunglasses can be extremely beneficial when driving as they reduce bright reflections of the cars ahead and the sun, and because they’re horizontally polarised they’re ideal for vertically polarised sunglasses.

This is because the surfaces you see on the car ahead such as the back window, rear door, roof are slanted towards you but the sun is more or less aligned in a vertical plain through both cars.

Polarising lenses therefore offer a greater definition of vision for driving by eliminating startling light effect and reducing eye fatigue.

What are the advantages of polarised lenses?

Polarised lenses have several distinct advantages over non-polarised lenses:

- Improves contrast and visual clarity

- Reduces eye strain

- Improves visual comfort

- Provides a true perception of colours

- Educes reflections and eliminates glare

Could polarised lenses pose a problem?

There are certain activities or sports for which polarised lenses aren’t the best sunglasses choice, including:

Skiing and icy conditions Polarised sunglasses make icy patches more difficult to spot, and you’ll need to be able to see them to avoid any potential hazards.

Seeing icy or oily patches on the road For exactly the same reason as above.

Viewing liquid crystal displays (LCDs) Polarised lenses can make some LCDs difficult to read.

How can I tell if my sunglasses are polarised?

Look through the sunglasses at the reflection of an object on a window panel and turn them around as if they’re the hands of a clock facing you. If the intensity of the reflection doesn’t change in relation to what you see through the window then the sunglasses aren’t polarised.

Do polarised sunglasses work better at different times of the day?

Yes, they do. The maximum level of polarisation is achieved when the sun is approximately 37 degrees from the horizon. If the sun is either very low or very high, sunglasses won’t be much help filtering glare in calm seas. A good rule of thumb is that polarised filters reduce the glare from calm waters for a sun altitude between 30 and 60 degrees.

Can you have clear polarising lenses?

Put simply, no. Because the very specific parallel row alignment of iodine crystals, clear lenses wouldn’t block light in a specific direction.

Are all polarising lenses the same?

Are all polarising lenses the same?

Not all polarisation is equal mainly due to the fact that not all polarised sunglasses block glare as well as they should, and a polarising filter is not a guarantee of an effective glare-blocking lens. This depends on how the lens has been produced and the quality of the filter.

Cheap polarised sunglasses, for example, might only eliminate 10% of reflected light, but the reality is that many people don’t realise there’s a difference in filter quality in sunglasses created by a better manufacturer.

At Discounted Sunglasses we stock a superb range of top brand designer sunglasses, many of which have polarized lenses.

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