Tuesday, February 21, 2006

Apple #150: Polarized Lenses

I just got some new sunglasses, and I had the lenses polarized. I've tried on polarized sunglasses before and didn't really see what the big deal is, but I trusted that it would do things that would be helpful for my eyes.

Now that I have a pair, though, I'm not sure I like them. They make everything yellow -- or at least the pair that I have does -- and this makes things seem brighter to me, not less bright. Also, I think polarization is supposed to reduce the glare of light when it glances off of surfaces, but I felt like I was getting shafts of light zinging into my eyeball all over the place.

So, how exactly does polarization work? Have I gotten myself a shoddy pair of sunglasses, or am I just too attached to my previous pair of sunglasses to recognize a good thing when it's right in front of my face?

  • Light is bouncing all over the place all the time. Light from the sun, light from lamps, reflected light, etc. These lightwaves are zinging and bouncing everywhere in all directions all the time.
  • Many types of surfaces can filter these random lightwaves so that only the lightwaves traveling in one particular plane can get through. When this filtering happens, it's called polarization.
  • The surface of a lake, for example, polarizes light waves. Most of the time, all you can see is the reflected glare off the surface, or light that does not make it through the filter that is the water. Sometimes, if you change your angle of vision relative to the surface of the lake, you can see better down into the water. This is because you are putting yourself closer in line with the path that the polarized light is taking through the water.
  • Polarized lenses have a chemical film that changes the way light travels after it strikes the lens. The lenses therefore will filter out any light that strikes the lens at the "wrong" angle.
  • Most of the glare that we find irritating or even painful is reflected light that bounces off chrome on cars or mirrors or water or the like. These surfaces are considered to be horizontal surfaces, and the light that bounces off those surfaces is similarly considered horizontal light. And because the surfaces tend to send the lightwaves that come toward it bouncing back in pretty much the same direction, those lightwaves have been polarized. So, all together, the annoying glares are all essentially horizontally polarized light.

  • The film on polarized lenses is structured so that it will filter out horizontally polarized light but will let in vertically polarized light. The thinking is that the glasses will remove the worst of glares but will still allow enough light to see by.

Two pair of polarized sunglasses placed at 90 degrees to each other will effectively block all light. (Image from Dave Jarvis' pages on Quantum Entanglement)

  • According to Howstuffworks, you can test lenses that are supposedly polarized. Hold the glasses in front of a reflective surface. The example they use is the hood of a car. I tried this with light coming through a juice glass and striking the counter, and also light from a desk lamp striking its base in a certain spot. Okay, with the glasses held in front of shiny places like these, rotate the glasses at least 90 degrees. You should see the glare diminish as you rotate. For a graphic that shows what is supposed to happen, go here and scroll down to the part on polarization.
  • When I tried this, I didn't notice any difference at all in the glare. I'm not convinced that this means that my sunglasses aren't actually polarized, however. When I was wearing them yesterday, I saw oily blotches on my back windshield that I wasn't able to see while wearing my regular glasses. Also when I drove past chain link fences, I felt like I could see through every little diamond-shaped opening in the fence.
  • Another website shows the difference between pictures taken with a polarized lens and pictures taken without it. In the pictures with the lens, the glare still existed, but it was quite reduced. So maybe I'm just being too demanding in thinking that my glasses should do more to cut the glare than they really can. But the way they turn everything yellow. It makes me squint.
  • Lots of people say that polarized lenses are great for activities like fishing because you can see more fish under the water with them. Other people say they cause lots of problems when riding motorcycles, especially if you have a helmet with a face shield.
  • So it looks like most people really like polarized lenses and that they do notice a pretty big, positive difference. I think this means maybe I'm just reluctant to change, or else that maybe I'd prefer a darker tint on my glasses as well as polarization. But I think I'll have to reserve that for another pair of sunglasses later in my hopefully more affluent future. For now, I think I'm just going to return these and get my money back.
Howstuffworks, How Sunglasses Work, especially the section on Polarization
Erin Morgan, Polarized Sunglasses, All About Vision.com
Tackle Tour, Apparel Review, Action Optics Seyschelle
Back Country Outlet, Polarized Sunglasses
Sport Touring.net Forums, problems with polarized glasses
Carnegie Mellon University, Robotic Search for Antarctic Meteorites, 1998

1 comment:

  1. The reason everything looks yellow most likely is because you purchased a amber/brown lens. The brown lens does brighten everything making yellows, greens, and whites pop more than other colors. If you want a truer tone when viewing through your sunglasses go with a gray or a green polarized lens. Gray and green give truer colors only with the polarization removing/eliminating most glare. I always tell my customers and yes I sell sunglasses (have for 6 years now) brown is awesome for an overcast day or if you plan on going golfing or like wearing your sunglasses into dusk. If your very light sensitive which I am, you need both the gray and brown. Gray for extremely bright days and brown for overcast. hope this helps.


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