Thursday, May 15, 2008

What are Polarized Lenses? Do I Need Polarized Lenses?

Polarized lenses are those that have had a layer of some type added to filter out polarized light. Simple enough. But what is polarized light and why does it matter?

How is your physics? Same as mine? Let’s keep this reasonable then. Basically, light is a wave which travels in a myriad of directions. Non-polarized light (from the sun, candles, etc.) waves vibrate in the same direction as the waves, or parallel to it. When light reflects off of some surfaces, it becomes polarized. The light wave now vibrates perpendicular (or horizontally) to the direction of the wave. When light reflects off shiny transparent surfaces it will become polarized. Some surfaces that will cause the polarization of light waves are water, concrete, metal, the side of a mountain and windows.

The effect of this is what we see as “glare”. Glare is just polarized light. These waves seem to over power the rest of the light in your normal field of view. Not only does experiencing glare result in discomfort, but it can be potential dangerous as your field of view becomes blocked. If you are driving, skiing, or doing any kind of sport, this could result in injury.

Many sunglasses companies have therefore added “polarized” lenses to their product lines. This is done is several ways, depending on the quality. The cheapest version is a coating, which is maybe effective at the beginning, but will wear off after being exposed to water or several cleanings. More professional sunglasses with put a filter in the actual lens. This filter essential blocks polarized light from entering your eye in a way similar to the following picture.

(Imagine light coming from the left, your eyes on the right, and the filter in between)

Now, polarized lenses are almost always more expensive than regular lenses, but I recommend them if you are going to be doing any activity near shiny transparent surfaces, which is ridiculous, because that covers most sports and activities.
This feature is not essential for fashion, some sporting activities and covering up red eyes, so it’s up to you to decide.

Photo courtesy of WikiMedia Commons

2 Responses to “What are Polarized Lenses? Do I Need Polarized Lenses?”

Polarized fan said...
October 5, 2009 at 2:53 AM

I have been working in the polarized lens / sunglass industry for over 20 years and I have never seen a sunglass with a polarized "coating". All polarized lenses contain a polarized film which is usualy "sandwiched" into the lens structure via lamination, injection moulding (as an insert) or casting. The "washing off" effect referred to is probably delamination caused by water or environmental attack. Any type of polarized lens can suffer from this given enough abuse.

Sunglasses Guy said...
October 5, 2009 at 7:40 AM

Hello Polarized fan,

Thanks for clearing up some of the technology behind this. I can always use help.

What exactly is casting? I've seen both the "sandwiched" and injection type.

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