Light Unpolarizer

coming out of them. Years ago I was getting gas and wearing polarized sunglasses. I couldn't see the display on the pump, I thought it was defunct actually, things break. But I look closer of course and my head tilts a bit and I begine to see it. So I tilt my head alot and of course it dawned on me. It was polarized the wrong way.

polarized sunglasses to work they must have a certain polar orientation. Glare contains more light of one polarization than the other because of being reflected at a somewhat oblique angle. It is "squished".

should have known which polarization NOT to use and designed accordingly. Oh yes it is far fetched to ask a guy to think of everything like that, but that's why they get the big bucks. I can bitch, but not draw and quarter the dude.

tinted, they are supposedly polarized. I know a little optics and I had a look at his glasses and I see one his main problem is astigmatism. Then he tells me they're polarized so I broke out my cellphone and looked through the lenses while turning, but it didn't darken. I'm thinking maybe they can't polarize it so well not tinted but that's bullshit because it just can't work that way.

unpolarizer. I'm sure that if an unpolarizer exists it would be in use because alot of people have polarized sunglasses. However I am having a hard time fathoming just how such a thing would work. In a way it would have to produce something that is not there.

yet aware. Would a diffuser unpolarize light ? Damifino.

the light still polarized when it hits the screen ?

was FUBARed IMO. The OP was talking about multiple filters and how if at 45 degrees and all this shit, bla bla bla.

yes, many things will undifuse polarized light, like plastic.

here's two photos of this

This was taken with a polarizer. The "black" background is a huge LCD monitor displaying bright white. The polarizer on the came is set to block this, but the empty plastic vial changes the polarization, making it show up as bright white.

Same effect here with some safety glasses, you can see the stresses in the lense against the frames as well

coming out of them. Years ago I was getting gas and wearing polarized sunglasses. I couldn't see the display on the pump, I thought it was defunct actually, things break. But I look closer of course and my head tilts a bit and I begine to see it. So I tilt my head alot and of course it dawned on me. It was polarized the wrong way.

polarized sunglasses to work they must have a certain polar orientation. Glare contains more light of one polarization than the other because of being reflected at a somewhat oblique angle. It is "squished".

should have known which polarization NOT to use and designed accordingly. Oh yes it is far fetched to ask a guy to think of everything like that, but that's why they get the big bucks. I can bitch, but not draw and quarter the dude.

tinted, they are supposedly polarized. I know a little optics and I had a look at his glasses and I see one his main problem is astigmatism. Then he tells me they're polarized so I broke out my cellphone and looked through the lenses while turning, but it didn't darken. I'm thinking maybe they can't polarize it so well not tinted but that's bullshit because it just can't work that way.

unpolarizer. I'm sure that if an unpolarizer exists it would be in use because alot of people have polarized sunglasses. However I am having a hard time fathoming just how such a thing would work. In a way it would have to produce something that is not there.

yet aware. Would a diffuser unpolarize light ? Damifino.

the light still polarized when it hits the screen ?

was FUBARed IMO. The OP was talking about multiple filters and how if at 45 degrees and all this shit, bla bla bla.

A polymer quarter-wave plate after the polarizer makes the output more or less circularly polarized, so that polaroid sunglasses pass half the light regardless of which way they're rotated. I don't know how fancy they get, but by using multiple layers of stretched polymer, you can make very nearly achromatic quarter wave plates. Otherwise the sunglasses would cause the colour to change slightly depending on which way the display was oriented.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Seriously excellent pics. It's not the cool lookingness of it, it's the way it was made. However does it prove that it unpolarizes the light or just g ives it a twist naturally, like an LCD would ?

Anything to do with circularly polarized light does nothing to answer this. I do find it an interesting subject though. Circularly polarized light is not likely to be usable by LCD displays because twisting the light would ma ke no differece.

At any rate, I am talking about something that actually unpolarizes polariz ed light. Does such a thing exist ? Those pictures don't prove it because u nder those test conditions all it has to do is twist a bit. It might be int eresting to see a motion video of that and have the cameraperson tilt the c amera one way and the other and see what happens.

J

Circular polarizers are commonly used for improving contrast on displays where (1) there are conductive shiny parts inside, and (2) the light is generated in the display (examples would be Nixie tubes and vacuum-fluorescents). Light that goes in gets circularly polarized, but when it is reflected from an electrical conductor the "rotation" is reversed and it can't get back out again. Light generated inside the display loses some intensity passing through the circular polarizer, but nowhere near as much as the reflected light. Circular polarizers are also used on some LCDs for similar reasons.

Light that has never been polarized has "waves" at all angles. After it's passed through a polarizer, the only waves that get through are all going the same way. Passing polarized light through various things can change the angle of the polarization, but I don't think it can be randomized again.

Isaac

was made. However does it prove that it unpolarizes the light or just gives it a twist naturally, like an LCD would ?

do find it an interesting subject though. Circularly polarized light is not likely to be usable by LCD displays because twisting the light would make no differece.

I do recall the plastic vial appeared bright in any angle, so it's safe to say is was unpolarizing light from any angle, and not just twisting it or whatever that would be called.

The safety glasses had to he held just right to get the glow effect.

I just tested a few more objects and the only things that consistently unpolarized or just diffused the light from the LCD monitor were polypropylene bags or objects like the good quality deli containers and antistatic plastic bags, the metallized ones. I'd like to try one of the many sheets of plastic as used in LCD panels, but behind the glass. They all have very odd properties.

Polarization is usually defined in terms of the E field direction, i.e. E_0 in the usual expression for a monochromatic plane wave,

E(x,t) = Re{E_0 exp(i(k dot x - omega*t) }, where x is the position vector (i.e. the location of the observation point in space) and k is the propagation vector, also called the spatial frequency vector.

The energy carried by any light beam is proportional to |E|**2. (Strictly speaking it's proportional to the vector cross product of E and H, but in any given linear medium, |H| is proportional to |E|.) E is a vector, so it has to have a direction and a nonzero magnitude at any instant if there's power flowing. (|E| can be zero if the polarization is exactly linear, but only for an instant.)

Thermal light has no time-averaged polarization, but that's because it's very broadband. Sunlight has a polarization vector that changes on the scale of a femtosecond or two.

Once the light has been put through a polarizer, there's no way to recover that very rapid variation, but there are various approximate methods for making "depolarizers".

For displays and other such things, circular polarizers are the most common sort of depolarizer, because they fix the polaroid sunglass problem, they're cheap, and that's all that's needed. Note that a circular polarizer so-called doesn't actually work analogously to a linear polarizer--it's a film polarizer laminated with a quarter-wave plate on one side, whereas in order for it to pass one helicity unaltered, it would need a waveplate on each side.

For display use, you put the waveplate on the outside, facing the viewer, so that it selects one linear polarization from the LCD as normal, and then converts it to circular, so that the viewer's sunglasses don't cause problems.

Other approaches sometimes used in instruments are rotating ground-glass diffusers, which make the polarization change on the scale of hundreds of microseconds at best, or Cornu depolarizers, which are waveplates whose retardation varies rapidly across the field of view. Cornu depolarizers are mostly used in grating spectrometers, where they can adequatly homogenize out the polarization dependence of the grating. They're not much use otherwise.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

e

Is it possible to see the polarized effect with the naked eye? On these types of glasses, I see the stresses at the corners where plastic is mounted as rainbow hues, very disturbing - interpret as cheapness.

no.

well, anything optical made out of plastic is cheap to start with. There's going to be streeses in mounted lenses. I've noticed it in glasse lenses in metal frames as well.

The human eye can "sort of" detect polarisation of light.

I can see it; it's easy with practice.

1) Clear blue sky near sunrise or sunset : Look vertically up and spin yourself around by moving your feet. You will look a tit, but it's the best way to see it easily.

2) LCD monitor. Large clear area of white background. Again, rotate your head, so your head is vertical (normal position), then horizontal, etc..

In both cases, you are looking for a yellow-ish "bow tie" shape, at the VERY CENTRE of your vision. The bits that aren't yellow, which bits also form a bow-tie shape, appear (very) slightly blue-ish. Personally, I find that the yellow is far easier to see than the blue.

Martin

Yes. A non-metallic reflective surface.

Thanks for the detail experiments!

Remembering back, years ago when driving in bright sunlight after a rainfall, I used to tilt my head back and forth and marvel at how the sheen of light reflecting off the wet pavement would change. Didn't correlate to polarized light, just thought the effect was 'interesting'

Does such a thing exist? Yes. A non-metallic reflective surface.

Hmmmmm. There are people here who know alot more about physics than I, but I do remember something about that. Most metals conduct and most conductors reflect light. I guess that means they are usually opaque ?

However any smooth surface can reflect.

Totally black plastic can be polished to a mirror finish and though it will reflect alot of light, you can still tell.

So is it that something that does not conduct electricity will do this ?

J

Nope. :)

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Then why was it that projecting 3D slides at home required a metallized screen?

Conductive and non-conductive reflective surfaces treat polarized light differently -- don't recall specifically how (been a looooong time). That's why polaroid sunglasses work differently for glare off a windshield or off a (chrome) bumper.

Isaac