question: What are those crazy patterns I see in glass when wearing polarized sunglasses?
comment: Stresses in the glass. As I recall, mechanical stresses in the glass cause changes in the optical qualities you can see with polarized light. Some car windows have really interesting patterns
passages: Wearers of polarized sunglasses will occasionally observe inadvertent polarization effects such as color-dependent birefringent effects, for example in toughened glass (e.g., car windows) or items made from transparent plastics, in conjunction with natural polarization by reflection or scattering. The polarized light from LCD monitors (see below) is very conspicuous when these are worn.
  
  Section::::Applications and examples.:Sky polarization and photography.
   Some models have polarized lenses, made of Polaroid polarized plastic sheeting, to reduce glare caused by light reflected from non-metallic surfaces such as water (see Brewster's angle for how this works) as well as by polarized diffuse sky radiation (skylight). This can be especially useful to see beneath the surface of the water when fishing.
   Another type of smart sunglasses uses adaptive polarization filtering (ADF). ADF-type smart sunglasses can change their polarization filtering characteristics at runtime. For example, ADF-type smart sunglasses can change from horizontal polarization filtering to vertical polarization filtering at the touch of a button.
  
  The lenses of smart sunglasses can be manufactured out of multiple adaptive cells, therefore different parts of the lens can exhibit different optical properties. For example the top of the lens can be electronically configured to have different polarization filter characteristics and different opacity than the lower part of the lens.
  
  Section::::Human Computer Interface (HCI) control input.
   BULLET::::- bloom surrounding objects in front of glare
  
  Sunglasses are often worn to reduce glare; polarized sunglasses are designed to reduce glare caused by light reflected from non-metallic surfaces such as water, glossy printed matter or painted surfaces. An anti-reflective treatment on eyeglasses reduces the glare at night and glare from inside lights and computer screens that is caused by light bouncing off the lens. Some types of eyeglasses can reduce glare that occurs because of the imperfections on the surface of the eye.
  
  Light field measurements can be taken to reduce glare with digital post-processing.
  
  Section::::Measurement.
   Polarized sunglasses use the principle of Brewster's angle to reduce glare from the sun reflecting off horizontal surfaces such as water or road. In a large range of angles around Brewster's angle, the reflection of "p"-polarized light is lower than "s"-polarized light. Thus, if the sun is low in the sky, reflected light is mostly "s"-polarized. Polarizing sunglasses use a polarizing material such as Polaroid sheets to block horizontally-polarized light, preferentially blocking reflections from horizontal surfaces. The effect is strongest with smooth surfaces such as water, but reflections from roads and the ground are also reduced.
   Section::::Improvements.
   Section::::Types of polarimeter.
  
  Section::::Types of polarimeter.:Laurent's half-shade polarimeter.
  
  When plane-polarised light passes through some crystals, the velocity of left-polarised light is different from that of the right-polarised light thus the crystals are said to have two refractive indices i.e. double refracting
   Section::::Applications and examples.
  
  Section::::Applications and examples.:Polarized sunglasses.
  
  Unpolarized light, after being reflected by a specular (shiny) surface, generally obtains a degree of polarization. This phenomenon was observed in 1808 by the mathematician Étienne-Louis Malus, after whom Malus's law is named. Polarizing sunglasses exploit this effect to reduce glare from reflections by horizontal surfaces, notably the road ahead viewed at a grazing angle.
   "Circular polarizers", also referred to as "circular polarizing filters", can be used to create circularly polarized light or alternatively to selectively absorb or pass clockwise and counter-clockwise circularly polarized light.
  
  They are used as polarizing filters in photography to reduce oblique reflections from non-metallic surfaces, and are the lenses of the 3D glasses worn for viewing some stereoscopic movies (notably, the RealD 3D variety), where the polarization of light is used to differentiate which image should be seen by the left and right eye.
  
  Section::::Circular polarizers.:Creating circularly polarized light.
   Smart sunglasses which are able to change their light filtering properties at runtime generally use liquid crystal technology. As lighting conditions change, for example when the user goes from indoors to outdoors, the brightness ratio also changes and can cause undesirable vision impairment. An attractive solution for overcoming this issue is to incorporate dimming filters into smart sunglasses which control the amount of ambient light reaching the eye. An innovative liquid crystal based component for use in the lenses of smart sunglasses is PolarView by LC-Tec. PolarView offers analog dimming control, with the level of dimming being adjusted by an applied drive voltage.
   BULLET::::- this change of the polarization state is converted into a change of intensity by dichroic absorption, usually by external dichroic polarizers.
  
  Section::::Activation.
  
  Liquid crystals can be aligned by both magnetic and electric fields. The strength of the required magnetic field is too high to be feasible for display applications.
  
  One electro-optical effect with LCs requires a current through the LC-cell; all other practiced electro-optical effects only require an electric field (without current) for alignment of the LC.
  
  Section::::Absorption Effects.
   A problem with Liquid Crystal Displays is that they use polarized light. If, for example, the user is wearing polarized sunglasses, the watch may be difficult to read because the plane of polarization of the display is roughly perpendicular to that of the glasses. If the light that illuminates the display is polarized, for example if it comes from a blue sky, the display may be difficult or impossible to read.
   The exact nature of the coating determines the appearance of the coated optic; common AR coatings on eyeglasses and photographic lenses often look somewhat bluish (since they reflect slightly more blue light than other visible wavelengths), though green and pink-tinged coatings are also used.
   A recent study on polarized light coherence leads to the development of new supports – the surfs – having contrast amplification properties for standard optical microscopy in cross polarizers mode. Made of optical layers on an opaque or transparent substrate, these supports do not modify the light polarization after reflection even if the numerical aperture of the incident source is important. This property is modified when a sample is present on a surf, a non-null light component is then detected after the analyzer rendering the sample visible.
   Much light is differentiated by polarization, e.g. light passing through crystals like sunstones (calcite) or water droplets producing rainbows. The polarization of the rainbow is caused by the internal reflection. The rays strike the back surface of the drop close to the Brewster angle.
   The polarizers can be set up in two geometrical configurations. One is a vertical/vertical (VV) geometry, where the second polarizer allows light through that is in the same direction as the primary polarizer. In vertical/horizontal (VH) geometry the second polarizer allows light not in same direction as the incident light.
  
  Section::::Description.
   As for AR coatings, HR coatings are affected by the incidence angle of the light. When used away from normal incidence, the reflective range shifts to shorter wavelengths, and becomes polarization dependent. This effect can be exploited to produce coatings that polarize a light beam. 
   The lenses of polarized sunglasses reduce glare reflected at some angles off shiny non-metallic surfaces, such as water. They allow wearers to see into water when only surface glare would otherwise be seen, and eliminate glare from a road surface when driving into the sun.
  
  Section::::Functions.:Protection.
  
  Sunglasses offer protection against excessive exposure to light, including its visible and invisible components.
   Gábor Horváth and his team have proposed that this new term needs to be better described and understood in order to better address the specific ecological consequences (direct or delayed in space and time) of light that was polarized (at source or by interacting with objects made or modified by humans).
   TSNIT is stand for Temporal – Superior – Nasal – Inferior-Temporal. This graph displays the thickness values along the Calculation Circle from T to S, N and back to T. The area of normal values is shaded. Measurements for the left eye are labeled "OS", those for the right eye "OD". 
  
  A defect is indicated if a measured value falls below the shaded area.
  
  Section::::GDx Comparative database.
   One of the simplest linear polarizers is the "wire-grid polarizer" (WGP), which consists of many fine parallel metallic wires that are placed in a plane. WGPs mostly reflect the non-transmitted polarization and can thus be used as polarizing beam splitters. The parasitic absorption is relatively high compared to most of the dielectric polarizers though much lower than in absorptive polarizers.
   BULLET::::- Polarized Light in Nature and Technology
  
  BULLET::::- Polarized Light Digital Image Gallery: Microscopic images made using polarization effects
  
  BULLET::::- Polarization by the University of Colorado Physics 2000: Animated explanation of polarization
  
  BULLET::::- MathPages: The relationship between photon spin and polarization
  
  BULLET::::- A virtual polarization microscope
  
  BULLET::::- Polarization angle in satellite dishes.
  
  BULLET::::- Using polarizers in photography
  
  BULLET::::- Molecular Expressions: Science, Optics and You — Polarization of Light: Interactive Java tutorial
  
  BULLET::::- Electromagnetic waves and circular dichroism: an animated tutorial
  
  BULLET::::- SPIE technical group on polarization
  
  BULLET::::- A Java simulation on using polarizers
  
  BULLET::::- Antenna Polarization
   The state of polarization of the light traveling through the LC layer cannot be perceived by human observers, it must be converted into intensity (e.g. luminance) in order to become perceivable. This is achieved with absorption by dichroic dyes and dichroic polarizers.
  
  Section::::Polymer Dispersed Liquid Crystals.
   Fresnel himself found this implication inconvenient; later that year he wrote:
   In binoculars with roof prisms the light path is split into two paths that reflect on either side of the roof prism ridge. One half of the light reflects from roof surface 1 to roof surface 2. The other half of the light reflects from roof surface 2 to roof surface 1. This causes the light to become partially polarized (due to a phenomenon called Brewster's angle). During subsequent reflections the direction of this polarization vector is changed but it is changed differently for each path in a manner similar to a Foucault pendulum. When the light following the two paths is recombined the polarization vectors of each path do not coincide. The angle between the two polarization vectors is called the "phase shift", or the geometric phase, or the Berry phase. This interference between the two paths with different geometric phase results in a varying intensity distribution in the image reducing apparent contrast and resolution compared to a porro prism erecting system. These unwanted interference effects can be suppressed by vapor depositing a special dielectric coating known as a "phase-correction coating" or "P-coating" on the roof surfaces of the roof prism. This coating corrects for the difference in geometric phase between the two paths so both have effectively the same phase shift and no interference degrades the image.
  