USE OF POLARIZATION IN THE FOLLOWING: MOVIE PRODUCTION TELEVISION SET SUN GLASSES ASTRONOMY

USE OF POLARIZATION IN MOVIES PRODUCTIONPolarization is also used in the entertainment industry to produce and

show 3-D movies. Three-dimensional movies are actually two movies

being shown at the same time through two projectors. The two movies

are filmed from two slightly different camera locations. Each individual

movie is then projected from different sides of the audience onto a metal

screen. The movies are projected through a polarizing filter. The

polarizing filter used for the projector on the left may have its polarization

axis aligned horizontally while the polarizing filter used for the projector

on the right would have its polarization axis aligned vertically.

Consequently, there are two slightly different movies being projected

onto a screen. Each movie is cast by light that is polarized with an

orientation perpendicular to the other movie. The audience then wears

glasses that have two Polaroid filters. Each filter has a different

polarization axis - one is horizontal and the other is vertical. The result of

this arrangement of projectors and filters is that the left eye sees the

movie that is projected from the right projector while the right eye sees

the movie that is projected from the left projector. This gives the viewer a

perception of depth.

RealD 3D cinema technology is a polarized 3D system that uses

circularly polarized light to produce stereoscopic image projection. The

advantage of circular polarization over linear polarization is that viewers

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are able to tilt their head and look about the theater naturally without

seeing double or darkened images.[2] However, as with other systems,

any significant head tilt will result in incorrect parallax and prevent the

brain from correctly fusing the stereoscopic images.

The high-resolution, digital cinema grade video projector alternately

projects right-eye frames and left-eye frames, switching between them

144 times per second.[2] The projector is either a Texas Instruments'

Digital Light Processing device or Sony's reflective LCOS (Liquid crystal

on silicon). A push-pull electro-optical liquid crystal modulator called a

ZScreen is placed immediately in front of the projector lens to alternately

polarize each frame. It circularly polarizes the frames clockwise for the

right eye and counter-clockwise for the left eye. The audience wears

circularly polarized glasses that have oppositely polarized lenses that

ensures each eye sees only its designated frame. In RealD Cinema,

each frame is projected three times to reduce flicker, a system called

triple flash. The source video is usually produced at 24 frames per

second per eye (total 48 frames/s), which may result in subtle ghosting

and stuttering on horizontal camera movements. A silver screen is used

to maintain the light polarization upon reflection and to reduce reflection

loss to counter some of the significant light loss due to polarization filter

absorption. The result is a 3D picture that seems to extend behind and in

front of the screen itself.[3]

They are not for use as sunglasses despite their dark tint. As a matter of

fact, the 3D technology is even worse than standard glasses, and posts

warnings on packaging that they are not safe for use as sunglasses.

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USE OF POLARIZATION IN TELEVISION SET

The polarization of an antenna refers to the orientation of the electric

field (E-plane) of the television set wave with respect to the Earth's

surface and is determined by the physical structure of the antenna and

by its orientation; note that this designation is totally distinct from the

antenna's directionality. Thus, a simple straight wire antenna will have

one polarization when mounted vertically, and a different polarization

when mounted horizontally. As a transverse wave, the magnetic field of

a radio wave is at right angles to that of the electric field, but by

convention, talk of an antenna's "polarization" is understood to refer to

the direction of the electric field.

Reflections generally affect polarization. For radio waves, one important

reflector is the ionosphere which can change the wave's polarization.

Thus for signals received following reflection by the ionosphere (a

skywave), a consistent polarization cannot be expected. For line-of-sight

communications or ground wave propagation, horizontally or vertically

polarized transmissions generally remain in the about the same

polarization state at the receiving location. Matching the receiving

antenna's polarization to that of the transmitter can make a very

substantial difference in received signal strength.

Polarization is predictable from an antenna's geometry, although in

some cases it is not at all obvious (such as for the quad antenna). An

antenna's linear polarization is generally along the direction (as viewed

from the receiving location) of the antenna's currents when such a

direction can be defined. For instance, a vertical whip antenna or WiFi

antenna vertically oriented will transmit and receive in the vertical

polarization. Antennas with horizontal elements, such as most rooftop

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TV antennas, are horizontally polarized (broadcast TV usually uses

horizontal polarization). Even when the antenna system has a vertical

orientation, such as an array of horizontal dipole antennas, the

polarization is in the horizontal direction corresponding to the current

flow. The polarization of a commercial antenna is an essential

specification.

Polarization is the sum of the E-plane orientations over time projected

onto an imaginary plane perpendicular to the direction of motion of the

radio wave. In the most general case, polarization is elliptical, meaning

that the polarization of the radio waves varies over time. Two special

cases are linear polarization (the ellipse collapses into a line) as we have

discussed above, and circular polarization (in which the two axes of the

ellipse are equal). In linear polarization the electric field of the radio wave

oscillates back and forth along one direction; this can be affected by the

mounting of the antenna but usually the desired direction is either

horizontal or vertical polarization. In circular polarization, the electric field

(and magnetic field) of the radio wave rotates at the radio frequency

circularly around the axis of propagation. Circular or elliptically polarized

radio waves are designated as right-handed or left-handed using the

"thumb in the direction of the propagation" rule. Note that for circular

polarization, optical researchers use the opposite right hand rule from

the one used by radio engineers.

It is best for the receiving antenna to match the polarization of the

transmitted wave for optimum reception. Intermediate matchings will lose

some signal strength, but not as much as a complete mismatch. A

circularly polarized antenna can be used to equally well match vertical or

horizontal linear polarizations. Transmission from a circularly polarized

antenna received by a linearly polarized antenna (or vice versa) entails a

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3dB reduction in signal-to-noise ratio as the received power has thereby

been cut in half.

USE OF POLARIZATION IN SUNGLASSES

Polarized sunglasses have been popular for years with boaters and

fishermen who need to reduce reflected glare from the water

surrounding them.

But now that many others who spend time outdoors have discovered the

benefits of polarized lenses, interest in these types of sunglasses has

soared.

Besides boaters, outdoor enthusiasts who benefit the most from

polarized sunglasses include skiers, bikers, golfers and joggers, all who

may enjoy a clearer view along with elimination of glare.

These sunglasses can be used for driving and, in fact, can reduce glare

from a long, flat surface such as the hood of the car or the road's

surface.

Polarized sunglasses also can be worn indoors by light-sensitive people,

including post-cataract surgery patients and those continually exposed to

bright light through windows.

How Do Polarized Lenses Work?

Light reflected from surfaces such as a flat road or smooth water

generally is horizontally polarized. This means that, instead of light being

scattered in all directions in more usual ways, reflected light generally

travels in a more horizontally oriented direction. This creates an

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annoying and sometimes dangerous intensity of light that we experience

as glare.

Polarized sunglasses cut glare and haze so your eyes are more

comfortable and you can see better.

Polarized lenses contain a special filter that blocks this type of intense

reflected light, reducing glare.

Though polarized sunglasses improve comfort and visibility, you will

encounter some instances when these lenses may not be advisable.

One example is downhill skiing, where you don't want to block light

reflecting off icy patches because this alerts skiers to hazards they are

approaching.

In addition, polarized lenses may reduce the visibility of images

produced by liquid crystal displays (LCDs) or light-emitting diode

displays (LEDs) found on the dashboards of some cars or in other

places such as the digital screens on automatic teller machines and self-

service gas pumps.

With polarized lenses, you also may be unable to see your cell phone or

GPS device.

Boaters and pilots also have reported similar problems when viewing

LCD displays on instrument panels, which can be a crucial issue when it

comes to making split-second decisions based strictly on information

displayed on a panel. (Some manufacturers of these devices have

changed their products to solve the problem, but many have not yet

done so.)

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However, for most other sports and activities, polarized sunglasses offer

great advantages. And today, many polarized lenses are available in

combination with other features that can enhance outdoor experiences.

Polarized bifocal sunglasses or progressive lenses are examples of

options for the presbyope who also likes outdoor sports.

And polarized photochromic lenses, which change from dark outside to

light inside, may be right for the light-sensitive person who frequently is

in and out of the sun on any given day.

USE OF POLARIZATION IN ASTRONOMY

Light Polarization is an important phenomenon in astronomy. The

polarization of starlight was first observed by the astronomers William

Hiltner and John S. Hall in 1949. Subsequently, Jesse Greenstein and

Leverett Davis, Jr. developed theories allowing the use of polarization

data to trace interstellar magnetic fields. Though the integrated thermal

radiation of stars is not usually appreciably polarized at source,

scattering by interstellar dust can impose polarization on starlight over

long distances. Net polarization at the source can occur if the

photosphere itself is asymmetric, due to limb polarization. Plane

polarization of starlight generated at the star itself is observed for Ap

stars (peculiar A type stars).

Both circular and linear polarization of light from the Sun has been

measured. Circular polarization is mainly due to transmission and

absorption effects in strongly magnetic regions of the Sun's surface.

Another mechanism that gives rise to circular polarization is the so-

called alignment-to-orientation mechanism. Continuum light is linearly

polarized at different locations across the face of the Sun (limb

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polarization) though taken as a whole, this polarization cancels. Linear

polarization in spectral lines is usually created by anisotropic scattering

of photons on atoms and ions which can themselves be polarized by this

interaction. The linearly polarized spectrum of the Sun is often called the

second solar spectrum. Atomic polarization can be modified in weak

magnetic fields by the Hanle effect. As a result, polarization of the

scattered photons is also modified providing a diagnostics tool for

understanding stellar magnetic fields.

Polarization is also present in radiation from coherent astronomical

sources (e.g. hydroxyl or methanol masers), and incoherent sources

such as the large radio lobes in active galaxies, and pulsar radio

radiation (which may, it is speculated, sometimes be coherent). Apart

from providing information on sources of radiation and scattering,

polarization also probes the interstellar magnetic field in our Galaxy as

well as in radio galaxies via Faraday rotation. In some cases it can be

difficult to determine how much of the Faraday rotation is in the external

source and how much is local to our own Galaxy, but in many cases it is

possible to find another distant source nearby in the sky; thus by

comparing the candidate source and the reference source, the results

can be untangled.

The polarization of the cosmic microwave background is also being used

to study the physics of the very early universe.

It has been suggested that as-tronomical sources of polarised light

caused the chirality found in biological molecules on Earth.

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