Polarized lenses and physics question

[Freshgeardude]

So, I just learned how polarized lenses work. If you don't know how they do, this question may be too complicated to answer. Maybe it is more obvious than I think.

So my question isn't how it works, but why is it when you look through another polarized glass(ie: car windows) you see patterns, like lines going through and these lines don't change places with change of angle you look at them, but they seem to fade darker or lighter instead.

Thanks in advance

 

[DisgruntledVirus]

God did it

 

[xSauronx]

Originally posted by: freshgeardude
So, I just learned how polarized lenses work. If you don't know how they do, this question may be too complicated to answer. Maybe it is more obvious than I think.

So my question isn't how it works, but why is it when you look through another polarized glass(ie: car windows) you see patterns, like lines going through and these lines don't change places with change of angle you look at them, but they seem to fade darker or lighter instead.

Thanks in advance

ghost-worms

 

[spaceman]

all polarized means is that they are made for the poles(north and south)
kinda like polar soda, polar bears,polar opposites and so forth.

 

[jorken]

Originally posted by: spaceman
all polarized means is that they are made for the poles(north and south)
kinda like polar soda, polar bears,polar opposites and so forth.

If I were a polar bear i'd wear polarized sunglasses.

 

[edro]

Originally posted by: jorken

Originally posted by: spaceman
all polarized means is that they are made for the poles(north and south)
kinda like polar soda, polar bears,polar opposites and so forth.

If I were a polar bear i'd wear polarized sunglasses.

LOL, you have succeeded in derailment.

 

[Freshgeardude]

Originally posted by: edro

Originally posted by: jorken

Originally posted by: spaceman
all polarized means is that they are made for the poles(north and south)
kinda like polar soda, polar bears,polar opposites and so forth.

If I were a polar bear i'd wear polarized sunglasses.

LOL, you have succeeded in derailment.

🙁

 

[speg]

I know how polarized lenses work but I don't know what you're talking about with the car windows... lines going through???

 

[PCTC2]

The patterns are just how they are manufactured or applied. It could be a variation of thickness of something (either the application or the film itself) that causes a phase shift in the light.
Light is a wave (and a particle, but for polarization, we can ignore this physical property). The electric field part is a sinusoidal wave, with the magnetic field part at a 90 degree angle. Polarization, we can ignore everything except for the electric field. Say you have a ray of light with the electric field in the Y axis. If you did't know, light travels slower in a material (such as water or soap or glass), than it does in a vacuum. When light hits the film (which has an index of refraction (n), which determines refraction entering the material and the speed of light (c/n), greater than 1), it gets phase shifted (sinusoidal wave) by pi. So picture a sinusoidal wave suddenly shifted by pi. When it enters the film and is reflected back from the glass, depending on the thickness, when reflected, it will either be aligned with the reflected wave or not. This is constructive (aligned) or destructive (unaligned by pi) interference. Same think would happen for the adhesive layer (if there is a small layer of air), and the glass, to a smaller degree. I don't know how tints are manufactured, but when you look through polarized glasses that are polarized in the Y axis, you only get light in the Y axis. This removes a lot of randomized reflections so you can possibly notice this effect more than without polarized glasses.

Notice, the rules of light and polarization are correct here, but I don't know enough about window tints and their manufacture and application to know what part causes the pattern. Anything about the patterns is pure speculation.

 

[Linflas]

Originally posted by: speg
I know how polarized lenses work but I don't know what you're talking about with the car windows... lines going through???

Here is what he is talking about.
I read somewhere a long time ago this had something to do with the manufacturing process used to make the car windows.

 

[Freshgeardude]

Originally posted by: Linflas

Originally posted by: speg
I know how polarized lenses work but I don't know what you're talking about with the car windows... lines going through???

Here is what he is talking about.
yea that is what I am talking about. I posted this on my phone, so I couldnt link a pic that easily.

Originally posted by: PCTC2
The patterns are just how they are manufactured or applied. It could be a variation of thickness of something (either the application or the film itself) that causes a phase shift in the light.
Light is a wave (and a particle, but for polarization, we can ignore this physical property). The electric field part is a sinusoidal wave, with the magnetic field part at a 90 degree angle. Polarization, we can ignore everything except for the electric field. Say you have a ray of light with the electric field in the Y axis. If you did't know, light travels slower in a material (such as water or soap or glass), than it does in a vacuum. When light hits the film (which has an index of refraction (n), which determines refraction entering the material and the speed of light (c/n), greater than 1), it gets phase shifted (sinusoidal wave) by pi. So picture a sinusoidal wave suddenly shifted by pi. When it enters the film and is reflected back from the glass, depending on the thickness, when reflected, it will either be aligned with the reflected wave or not. This is constructive (aligned) or destructive (unaligned by pi) interference. Same think would happen for the adhesive layer (if there is a small layer of air), and the glass, to a smaller degree. I don't know how tints are manufactured, but when you look through polarized glasses that are polarized in the Y axis, you only get light in the Y axis. This removes a lot of randomized reflections so you can possibly notice this effect more than without polarized glasses.

Notice, the rules of light and polarization are correct here, but I don't know enough about window tints and their manufacture and application to know what part causes the pattern. Anything about the patterns is pure speculation.

I think this is the explanation I needed. thank you!

 

[biggestmuff]

Text

 

[Paperdoc]

Maybe this is close to the answer. "Natural" light is non-polarized - that is, the wave vibrations occur in nearly equal amounts in all directions perpendicular to the path of light travel. Polarizing lenses simply block most of this light and allow through only the waves vibrating in one plane, or more precisely in a narrow range of planes. If you take the light that has already passed though one polarizer and then run it through another, how much light gets through both of them depends on the alignment of the polarization planes of the two lenses. Perfectly aligned, all the light through the first lens also passes through the second. Aligned exactly perpendicular to each other, none of the light gets though both lenses.

In the real world, light that is reflected off a flat surface is largely polarized, usually in the plane of the surface. So using polarized sunglasses (which are made with their plane of polarization about 45 degrees from horizontal) substantially blocks bright reflections from horizontal surfaces like roads, water, etc. This selective removal of bright light improves your ability to see the rest of the natural unpolarized light.

Now, there's another way that light can end up polarized. Many crystalline materials will polarize light because the regular arrangement of atoms and molecules in the crystal selectively absorbs light only at certain angles, and lets the rest pass through. In fact, that is how they make polarized sunglasses in the first place - the lenses are made from a plastic in which the molecules are all oriented the same way, making it like a crystalline structure as far as its interaction with light goes.

Glass is an oddity. It looks clear and hard, and shatters into sharp-edged pieces when hit. We think of it as a crystalline material. So you might expect it to polarize light. But in fact, glass is really a supercooled fluid which flows EXTREMELY slowly, and it does NOT have a crystalline ordered structure, so it does not polarize light passing through it. Sure, light that is REFLECTED off its flat surface will be polarized, and those sunglasses will reduce the glare from glass surfaces. But light coming through the glass is not affected. In fact, in many applications it is important after working with glass to be sure it is non-crystalline everywhere, because a crystalline area will break more easily than a more flexible non-crystalline area.

And therein lies the explanation. As others have said here, in the production of glass for automobiles, especially rear and side windows, manufacturers deliberately try to make glass with lots of crystalline zones in them. The idea is that, once it starts to break under impact, you want it to shatter into thousands of small pieces flying off in different directions. You do NOT want it breaking into large plates with sharp edges, because those would have much higher mass and momentum per piece and they will cut people badly. So how do they do that? They shape the glass, then heat it to just the right temperature, and then blast cold air on it to chill it rapidly. This actually causes the atoms it the glass to crystallize in local zones, although not to make one large uniform crystal network. Often, and especially for complex shapes like rear windows, the cooling is done with a stationary array of air jets. The result is that the cooling and crystallizing is concentrated at the locations of the regularly-spaced jets. So the window ends up with a pattern of semi-crystalline zones that do polarize light coming through them, surrounded by non-crystalline zones that do not polarize light. When you look at light coming through such a window while you're wearing polarized sunglasses, you see bright and darker areas in a regular array that discloses where the cooling air jets were.