Issues with polarized sunglasses?

7:54 a.m. on November 15, 2010 (EST)
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Maybe I'm crazy but it sure seems like my polarized sunglasses create depth-of-field issues, particularly when hiking on leaf-covered trails.

I did all my hiking in California before moving to the Southeast so there wasn't much opportunity for hiking in the kind of leaf cover we get in North Carolina. I noticed on a very faint trail last month that the glasses seemed to be affecting my ability to discern the subtle indention in the soil caused by a trail underneath it.

Yesterday I was out in a state park with well-marked trails and kept having the same issues of not being able to judge where the trail is.

Just thought I'd throw this out there and see if anyone else out there has had a similar experience.

2:52 p.m. on November 15, 2010 (EST)
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The purpose of polarized sunglasses is to cut glare. The major problem with polarized sunglasses is that they cut glare. Sounds like a non sequitor and maybe self-contradictory.

One of the ways we spot slick places (wet or icy spots) that we might slip on and other clues about the surfaces we walk on is the reflected and scattered light. On horizontal surfaces, the reflected light is horizontally polarized. Polarized sunglasses have their polarization oriented vertically. The result is that the clues we might get from the reflected light are reduced or eliminated. In your case, this included clues for the indentation of the trail.

A few years back, one of the car enthusiast magazines ran some tests using polarized sunglasses on experienced race drivers on a track where water was used to produce slippery areas. They found that the drivers' lap times were significantly slower because of the difficulty in judging the slippery areas, since the polarization cut the glare that cued the location and extent of the water-covered, more slippery areas. I have seen one article where a similar test was done on a ski slope. The effect was less, because (according to the article) ski slopes are a mixture of angles, plus the snow crystals are at a variety of angles, so there is a wide range of polarization in the light reflected and scattered from the surface.

Polarized glasses are fine for the beach, boating, fishing, and other activities where cutting the reflections is beneficial.

3:23 p.m. on November 15, 2010 (EST)
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I agree Bill.  Also looking at digital gadgets like bike computers, altimeters and digital watches is a pain with polarized glasses.  Evidentally, the lenses on these gadgets are also polarized and at some angles the polarized surfaces match up just right and you can't read your digital gadget at all. 

I used to wear them when I was in law enforcemen b/c you could see into vehicles better and tell what the driver was doing since the window glare was cancelled by the polarizing affect.  That and fishing are all I can recommend them for. 

4:42 p.m. on November 15, 2010 (EST)
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Thanks, Bill, I figured you'd know what the deal was.

 

7:21 p.m. on November 15, 2010 (EST)
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... Also looking at digital gadgets like bike computers, altimeters and digital watches is a pain with polarized glasses.  Evidentally, the lenses on these gadgets are also polarized and at some angles the polarized surfaces match up just right and you can't read your digital gadget at all. 

Actually, the problem is the way LCDs work. The "liquid crystals" change their polarization according to the electric voltage supplied. So each segment of a number or letter, for example, has the two layers cross-polarized to block the light passing through (backlit display, as used in night mode) or reflected (day mode, or as used with most monochrome displays). In short, the LCD depends on polarized light to work, and your polarizing glasses end up being cross-polarized to some or all parts of the display.

Here are two shots of a computer screen (LCD) with a linear polarizing filter at two orientations at right angles -

Polarizer orthogonal to screen polarization
PolarExpt_3.jpg

 

Polarizer parallel to screen polarization
PolarExpt_4.jpg

So, when you are having a hard time reading the screen on your LCD widget, try rotating your head at right angles (or the widget, whichever is easier).

7:32 p.m. on November 15, 2010 (EST)
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Thanks for the clarification.  I knew it was something withthe LCDs but never knew exactly why.  I just forego polarized glasses altogether except when I am fishing.

11:20 p.m. on November 15, 2010 (EST)
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I've seen this too: I have a 24" iMac whose screen goes black when I wear my polarized shades.

September 21, 2014
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