Cathode Ray Tube
A CRT monitor works in a similar manner to an old-fashioned television. It has a glass screen coated in dots of red, green or blue phosophor. The monitor aims an electron beam across the inside of the screen, covering the whole screen, one row at a time. Depending on the image, the electron beam varies in strength, depending on which dot it is passing over. This happens fast enough that the user appears to see a solid image with some dots illuminated and othe...rs not, thus creating the picture.
An LCD monitor also breaks the picture down into dots and recreates it. However, it works by shining light through two sheets (usually plastic) with a layer of liquid crystal between them. The sheets are polarized in a perpendicular manner, meaning that the light which passes through the inside sheet cannot pass through the outside sheet without manipulation. This manipulation comes from the individual crystals which, in response to an electrical charge, can change the direction of the light passing through and, in turn, cause it to pass through the outside sheet and become visible. The actual outside of the monitor can be glass or plastic and is simply a transparent protective layer to prevent damage to the polarized sheets. An LED screen is simply a version of an LCD screen that uses LEDs to shine the light through the polarized sheets and crystals.
One of the most common LC phases is the nematic. The word nematic comes from the Greek νήμα (Greek: nema), which means "thread". This term originates from the thread-like topological defects observed in nematics, which are formally called 'disclinations'. Nematics also exhibit so-called "hedgehog" topological defects. In a nematic phase, the calamitic or rod-shaped organic molecules have no positional order, but they self-align to have long-range directional order with their long axes roughly parallel. Thus, the molecules are free to flow and their center of mass positions are randomly distributed as in a liquid, but still maintain their long-range directional order. Most nematics are uniaxial: they have one axis that is longer and preferred, with the other two being equivalent (can be approximated as cylinders or rods). However, some liquid crystals are biaxial nematics, meaning that in addition to orienting their long axis, they also orient along a secondary axis. Nematics have fluidity similar to that of ordinary (isotropic) liquids but they can be easily aligned by an external magnetic or electric field. Aligned nematics have the optical properties of uniaxial crystals and this makes them extremely useful in liquid crystal displays (LCD).
Electric and magnetic field effects. The ability of the director to align along an external field is caused by the electric nature of the molecules. Permanent electric dipoles result when one end of a molecule has a net positive charge while the other end has a net negative charge. When an external electric field is applied to the liquid crystal, the dipole molecules tend to orient themselves along the direction of the field.Even if a molecule does not form a permanent dipole, it can still be influenced by an electric field. In some cases, the field produces slight re-arrangement of electrons and protons in molecules such that an induced electric dipole results. While not as strong as permanent dipoles, orientation with the external field still occurs. The effects of magnetic fields on liquid crystal molecules are analogous to electric fields. Because magnetic fields are generated by moving electric charges, permanent magnetic dipoles are produced by electrons moving about atoms. When a magnetic field is applied, the molecules will tend to align with or against the field.Surface preparationsIn the absence of an external field, the director of a liquid crystal is free to point in any direction. It is possible, however, to force the director to point in a specific direction by introducing an outside agent to the system. For example, when a thin polymer coating (usually a polyimide) is spread on a glass substrate and rubbed in a single direction with a cloth, it is observed that liquid crystal molecules in contact with that surface align with the rubbing direction. The currently accepted mechanism for this is believed to be an epitaxial growth of the liquid crystal layers on the partially aligned polymer chains in the near surface layers of the polyimide.Fredericks transition. The competition between orientation produced by surface anchoring and by electric field effects is often exploited in liquid crystal devices. Consider the case in which liquid crystal molecules are aligned parallel to the surface and an electric field is applied perpendicular to the cell. At first, as the electric field increases in magnitude, no change in alignment occurs. However at a threshold magnitude of electric field, deformation occurs. Deformation occurs where the director changes its orientation from one molecule to the next. The occurrence of such a change from an aligned to a deformed state is called a Fredericks transition and can also be produced by the application of a magnetic field of sufficient strength.The Fredericks transition is fundamental to the operation of many liquid crystal displays because the director orientation (and thus the properties) can be controlled easily by the application of a field.
"Computer screens and television sets work on similar principles. Both produce static electric fields and alternating electric and magnetic fields at various frequencies.However, screens with liquid crystal displays used in some laptop computers and desktop units do not give rise to significant electric and magnetic fields.Modern computers have conductive screens which reduce the static field from the screen to a level similar to that of the normal background in the home or workplace.At the position of operators (30 to 50 cm from the screen), alternating magnetic fields are typically below 0.7 µT in flux density (at power frequencies). Alternating electric field strengths at operator positions range from below 1 V/m up to 10 V/m."
Each pixel on a computer screen is composed of three small dots of compounds called phosphors surrounded by a black mask. The phosphors emit light when struck by the electron beams produced by the electron guns at the rear of the tube. The three separate phosphors produce red, green, and blue light, respectively.
A backlight is a form of illumination used in liquid crystal displays (LCDs). As LCDs do not produce light by themselves (unlike for example Cathode ray tube (CRT) displays), they need illumination (ambient light or a special light source) to produce a visible image. Backlights illuminate the LCD from the side or back of the display panel, unlike frontlights, which are placed in front of the LCD. Backlights are used in small displays to increase readability in low light conditions such as in wristwatches, and are used in smart phones, computer displays and LCD televisions to produce light in a manner similar to a CRT display
Electroluminescence is the result of radiative recombination of electrons and holes in a material, usually a semiconductor. The excited electrons release their energy as photons - light. Prior to recombination, electrons and holes may be separated either by doping the material to form a p-n junction (in semiconductor electroluminescent devices such as light-emitting diodes) or through excitation by impact of high-energy electrons accelerated by a strong electric field (as with the phosphors in electroluminescent displays).
A fluorescent or electroluminescent light source (or backlight) (1), occupies the panel's rear. (In a few new models, the backlighting source is a row of LEDs around the perimeter of the screen.) In front of it are two glass-mounted polarizing filters (2) and (5), scored with super-fine parallel grooves and oriented with their grooves facing and rotated 90 degrees to each other. (A polarizing filter allows light waves to pass or not pass, depending on the waves' orientation; those waves that do pass are thus oriented in a known plane.) The filters lie a tiny distance apart, and a layer of liquid-crystal molecules (3) is sandwiched between them.Liquid crystals, by their nature, arrange themselves in predictable structures. Here, the molecules' natural tendency is to lie parallel with the grooves in the filters, with the excess molecules suspending themselves in the tiny space between the filters, arranging themselves in a helical arrangement. When light from the backlight (polarized by the rear filter) hits a given helix, it follows the path of the molecules and is "twisted" in the proper direction to pass through the front polarizing filter and on to your eye. (If the light was not twisted, the front filter would partially or wholly block it.)Now, introduce a transparent, thin grid of transistors (4) that can apply current at any given intersection of the grid, with each intersection representing a "subpixel." Each pixel in a color LCD employs three addressable subpixels (red, green, and blue) fronted by a matching color filter. Charge a given transistor, and there the crystal arrangement "untwists," redirecting the local orientation of light before it reaches the color filters and the front polarizing filter. Depending on its orientation, the light in each subpixel may pass, pass partially, or be blocked; by precisely regulating the transistor charges, the display controls how much light can reach a pixel's three individual color filters and exit the front polarizing filter as visible light (6).Because the eye perceives any given set of three subpixels as a single color dot, you simply see a pixel as a dot of blended color; therefore, varying the pixels' ratios of red, green, and blue creates the illusion of individually colored pixels. Now, multiply this operation by hundreds of thousands—possibly more than a million—pixels, performed many times per second
"As a 23-year-old German university student, Paul Julius Gottlieb Nipkow proposed and patented the Nipkow disk in 1884. This was a spinning disk with a spiral pattern of holes in it, so each hole scanned a line of the image. Although he never built a working model of the system, variations of Nipkow's spinning-disk "image rasterizer" became exceedingly common. Constantin Perskyi had coined the word television in a paper read to the International Electricity Congress at the International World Fair in Paris on August 25, 1900. Perskyi's paper reviewed the existing electromechanical technologies, mentioning the work of Nipkow and others. However, it was not until 1907 that developments in amplification tube technology, by Lee de Forest and Arthur Korn among others, made the design practical.The first demonstration of the instantaneous transmission of images was by Georges Rignoux and A. Fournier in Paris in 1909. A matrix of 64 selenium cells, individually wired to a mechanical commutator, served as an electronic retina. In the receiver, a type of Kerr cell modulated the light and a series of variously angled mirrors attached to the edge of a rotating disc scanned the modulated beam onto the display screen. A separate circuit regulated synchronization. The 8x8 pixel resolution in this proof-of-concept demonstration was just sufficient to clearly transmit individual letters of the alphabet. An updated image was transmitted "several times" each second.
In 1911, Boris Rosing and his student Vladimir Zworykin created a system that used a mechanical mirror-drum scanner to transmit, in Zworykin's words, "very crude images" over wires to the "Braun tube" (cathode ray tube or "CRT") in the receiver."
IBM Research Headquarters Yorktown Heights New York
"The Yorktown Heights building, situated on private land not generally accessible to the public, is a large crescent-shaped structure consisting of three levels with 40 aisles each, radiating out from the center of the circle described as the crescent. Due to this construction, none of the offices have windows. The lowest level is partially underground in some areas toward the shorter side of the crescent, which also leads to the employee parking lots. A large overhang protrudes from the front entryway of the building, and faces the visitor parking lot. The building houses a library, an auditorium and a cafeteria. It was designed by the architect Eero Saarinen and built in 1956–1961"