A liquid crystal display or LCD (English acronym for Liquid Crystal Display) is a thin, flat screen consists of a number of color or monochrome pixels arranged in front of a light source or reflector . It is often used in electronic devices battery because it uses very small amounts of electricity.
Features
Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes, and two filters polarization transmission axes of each are (in most cases) perpendicular to each other. No liquid crystal between the polarizing filter, the light passing through the first filter would be blocked per second (crossed) polarizer.
surface electrodes in contact with the liquid crystal material is treated to adjust the liquid crystal molecules in a particular direction. This treatment usually consists of a thin polymer layer that is unidirectionally rubbed using, for example, cloth. The direction of liquid crystal alignment is defined by the direction of rubbing.
Before applying an electric field, the orientation of liquid crystal molecules is determined by adaptation to surfaces. In a twisted nematic device, TN, (some more devices common for liquid crystal display), the directions of surface alignment of the two electrodes are perpendicular to each other, and so molecules are arranged in a helical structure, or kink. Because the liquid crystal material is birefringent, light passing through a polarizing filter is rotated by the liquid crystal helix passing through the liquid crystal layer, allowing it to pass through the second polarizing filter . Half of the incident light is absorbed by the first polarizing filter, but otherwise the entire assembly is transparent.
When a voltage is applied across the electrodes, a nut adjusts the liquid crystal molecules parallel to the electric field that distorts the helical structure (this is resisted by elastic forces since the molecules are confined to surfaces.) This reduces the rotation of the polarization of the incident light, and the device appears gray. If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almost completely peeled and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light is mainly polarized perpendicular to the second filter, and so will be blocked and the pixel appears black. By controlling the voltage applied across of the liquid crystal layer in each pixel, light can be allowed to pass through different amounts, constituting the different shades of gray.
Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes, and two filters polarization transmission axes of each are (in most cases) perpendicular to each other. No liquid crystal between the polarizing filter, the light passing through the first filter would be blocked per second (crossed) polarizer.
surface electrodes in contact with the liquid crystal material is treated to adjust the liquid crystal molecules in a particular direction. This treatment usually consists of a thin polymer layer that is unidirectionally rubbed using, for example, cloth. The direction of liquid crystal alignment is defined by the direction of rubbing.
Before applying an electric field, the orientation of liquid crystal molecules is determined by adaptation to surfaces. In a twisted nematic device, TN, (some more devices common for liquid crystal display), the directions of surface alignment of the two electrodes are perpendicular to each other, and so molecules are arranged in a helical structure, or kink. Because the liquid crystal material is birefringent, light passing through a polarizing filter is rotated by the liquid crystal helix passing through the liquid crystal layer, allowing it to pass through the second polarizing filter . Half of the incident light is absorbed by the first polarizing filter, but otherwise the entire assembly is transparent.
When a voltage is applied across the electrodes, a nut adjusts the liquid crystal molecules parallel to the electric field that distorts the helical structure (this is resisted by elastic forces since the molecules are confined to surfaces.) This reduces the rotation of the polarization of the incident light, and the device appears gray. If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almost completely peeled and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light is mainly polarized perpendicular to the second filter, and so will be blocked and the pixel appears black. By controlling the voltage applied across of the liquid crystal layer in each pixel, light can be allowed to pass through different amounts, constituting the different shades of gray.
OPERATION Operation of these screens are based on the use of substances that share properties of solids and liquids at a time. When a light beam crosses a particle of these substances must necessarily follow the empty space between molecules, as you would when crossing a solid crystal-but each of these particles can be applied electric current to change its polarization letting the light or not. An LCD display consists of two polarizing filters placed perpendicular to one another so that by applying an electric current to the second one we will pass or not the light that has passed through the former. To get the color filters need to apply three more for each of the basic colors-red, green and blue-and reproduction of various shades of color, should apply different levels of brightness intermediate between light and no-light, This is accomplished with changes in the voltage applied to the filters. Benefits of such screens are its smaller size, low power-so used in laptops, and the disappearance of flicker problems and geometry of the normal screen CRT.
The disadvantages are its cost significantly higher than conventional monitors, the lower viewing angle-you have to look at the forehead, lower refresh rate and the loss in the range of colors so that no are suitable for design gráfico.A when buying one to buy one of these screens have to look, especially on these characteristics: the maximum resolution, we determined both by the number of liquid crystal cells actually exist on the screen.
Specifications
Important factors to consider when evaluating an LCD monitor:
Resolution: horizontal and vertical size expressed in pixels ( eg 1024x768). Unlike CRT monitors, LCD screens have a resolution in support for best display effect.
point Width: The distance between the centers of two adjacent pixels. The smaller the width of a point, lower granularity in the image. The width of the point may be the same both vertically and horizontally, or different (less common).
Size: The size of an LCD panel measured on the diagonal (more specifically known as active viewing area).
Response Time: The minimum time required to change the color of a pixel or brightness. The response time is also divided into rise and fall time.
Matrix Type: active or passive.
angle: more specifically known as viewing direction.
Color Support: How many kinds of colors are supported?, Known as gamma color. Brightness: The amount of light emitted from the screen, also known as light.
Contrast: The ratio of intensity between the brightest and the darkest.
Appearance: The ratio of the width and height (eg, 4:3, 16:9 and 16:10).
Ports of Entry: among them are DVI, VGA, LVDS, or S - Video and HDMI.
Matrices active and passive targeting
LCDs LCDs with a small number of sectors, such as those used in digital watches and pocket calculators, have individual electrical contacts for each segment. An external dedicated circuit supplies an electric charge to control each segment. This structure is difficult to visualize for some display devices.
Small monochrome displays such as those found in personal organizers, or older laptop screens have a passive matrix structure which used technologies such as super-twisted nematic (STN) or double-layer STN (DSTN), ( DSTN corrects the problem of changing color STN) and color STN (CSTN) (a technology where the color is added using an internal color filter). Each row or column screen has a single electrical circuit. The pixels are addressed by both directions of row and column. This type of display is called passive-matrix addressed because the pixel must retain its state between refresh periods without benefit of a constant electric charge. As the number of pixels (and therefore columns and rows) increases, this type of display becomes less appropriate. Slow response times and a rather poor contrast are typical of passive matrix LCDs targeting.
In color devices such as modern high-resolution LCD monitors and televisions use an active matrix structure. An array of thin-film transistors (TFTs) is added to the polarization and color filters. Each pixel has its own dedicated transistor, allowing each column line to access one pixel. When a row line is activated, all column lines are connected to a row of pixels and the correct voltage is driven all the column lines. When the row line is deactivated, the next row line is activated. All row lines are activated sequentially during an active matrix actualización.La operation is directed to devices with higher brightness and size that is directed to passive matrix (targeting small devices, and in general, have faster response times, producing images much better.)
LCDs LCDs with a small number of sectors, such as those used in digital watches and pocket calculators, have individual electrical contacts for each segment. An external dedicated circuit supplies an electric charge to control each segment. This structure is difficult to visualize for some display devices.
Small monochrome displays such as those found in personal organizers, or older laptop screens have a passive matrix structure which used technologies such as super-twisted nematic (STN) or double-layer STN (DSTN), ( DSTN corrects the problem of changing color STN) and color STN (CSTN) (a technology where the color is added using an internal color filter). Each row or column screen has a single electrical circuit. The pixels are addressed by both directions of row and column. This type of display is called passive-matrix addressed because the pixel must retain its state between refresh periods without benefit of a constant electric charge. As the number of pixels (and therefore columns and rows) increases, this type of display becomes less appropriate. Slow response times and a rather poor contrast are typical of passive matrix LCDs targeting.
In color devices such as modern high-resolution LCD monitors and televisions use an active matrix structure. An array of thin-film transistors (TFTs) is added to the polarization and color filters. Each pixel has its own dedicated transistor, allowing each column line to access one pixel. When a row line is activated, all column lines are connected to a row of pixels and the correct voltage is driven all the column lines. When the row line is deactivated, the next row line is activated. All row lines are activated sequentially during an active matrix actualización.La operation is directed to devices with higher brightness and size that is directed to passive matrix (targeting small devices, and in general, have faster response times, producing images much better.)
Disadvantages
LCD technology still has some disadvantages compared to other display technologies:
While CRTs are capable of displaying multiple video resolutions without introducing artifacts, LCDs produce crisp images only in its "native resolution" and, sometimes, in fractions of the original resolution. When trying LCD panels to run non-native resolutions usually results in the panel on the scale of the image, the image blurring introduced or blocks and, in general, is susceptible to various kinds of HDTV blur. Many LCDs are not able to show ways of low-resolution screen (eg 320x200), because of these limitations of scale.
Although LCDs typically have more vibrant images and better contrast "real world" (the ability to maintain contrast and variation of color in bright environments) than CRTs, they have less contrast than CRTs in terms of the depth of blacks . Contrast is the difference between a full-on (white) and off-pixel (Black), and LCDs can have "backlight bleed" where light (usually seen from the corner of the screen) leaks and leaks in black becomes gray. In December 2007, the best LCDs can approach the contrast of plasma displays in terms of delivering deep black, but most LCDs still lag behind.
LCDs often have slower response times than their plasma and CRT, especially the old screens, creating ghost images when images are loaded quickly. For example, when moving the mouse quickly on an LCD, multiple cursors can be seen. Some LCD screens have
important contributions late. If the delay is large enough, that screen may be inadequate for operations fast and accurate mouse (CAD, FPS gaming) as compared to CRT or LCD monitors, small and insignificant amounts of input lag. Short running late are often highlighted in marketing.
LCD panels tend to have a limited viewing angle in relation to CRTs and plasma screens. This reduces the number of people who can easily see the same image - laptop screens are an excellent example. Thus, this lack of radiation is what gives its LCDs reduced power consumption compared with plasma displays and CRTs. While the viewing angles have improved to the point that it is rare that the colors are totally wrong in normal usage, at distances typical use of a computer LCDs still allow small changes in the user's posture, and even different positions between your eyes produce a significant color distortion, even the best LCDs on the market.
LCD monitors tend to be more fragile than their CRT. The screen may be especially vulnerable due to lack of a thick glass shield as in CRT monitors.
The dead pixels occur frequently and few manufacturers replace screens with dead pixels free.
horizontal bands and / or vertical are a problem in some LCD screens. This defect occurs as part of the manufacturing process, and can not be repaired (not a complete replacement of the screen). The bands can vary considerably even among LCD screens of the same make and model. The grade is determined by the manufacturing quality control procedures.
LCD technology still has some disadvantages compared to other display technologies:
While CRTs are capable of displaying multiple video resolutions without introducing artifacts, LCDs produce crisp images only in its "native resolution" and, sometimes, in fractions of the original resolution. When trying LCD panels to run non-native resolutions usually results in the panel on the scale of the image, the image blurring introduced or blocks and, in general, is susceptible to various kinds of HDTV blur. Many LCDs are not able to show ways of low-resolution screen (eg 320x200), because of these limitations of scale.
Although LCDs typically have more vibrant images and better contrast "real world" (the ability to maintain contrast and variation of color in bright environments) than CRTs, they have less contrast than CRTs in terms of the depth of blacks . Contrast is the difference between a full-on (white) and off-pixel (Black), and LCDs can have "backlight bleed" where light (usually seen from the corner of the screen) leaks and leaks in black becomes gray. In December 2007, the best LCDs can approach the contrast of plasma displays in terms of delivering deep black, but most LCDs still lag behind.
LCDs often have slower response times than their plasma and CRT, especially the old screens, creating ghost images when images are loaded quickly. For example, when moving the mouse quickly on an LCD, multiple cursors can be seen. Some LCD screens have
important contributions late. If the delay is large enough, that screen may be inadequate for operations fast and accurate mouse (CAD, FPS gaming) as compared to CRT or LCD monitors, small and insignificant amounts of input lag. Short running late are often highlighted in marketing.
LCD panels tend to have a limited viewing angle in relation to CRTs and plasma screens. This reduces the number of people who can easily see the same image - laptop screens are an excellent example. Thus, this lack of radiation is what gives its LCDs reduced power consumption compared with plasma displays and CRTs. While the viewing angles have improved to the point that it is rare that the colors are totally wrong in normal usage, at distances typical use of a computer LCDs still allow small changes in the user's posture, and even different positions between your eyes produce a significant color distortion, even the best LCDs on the market.
LCD monitors tend to be more fragile than their CRT. The screen may be especially vulnerable due to lack of a thick glass shield as in CRT monitors.
The dead pixels occur frequently and few manufacturers replace screens with dead pixels free.
horizontal bands and / or vertical are a problem in some LCD screens. This defect occurs as part of the manufacturing process, and can not be repaired (not a complete replacement of the screen). The bands can vary considerably even among LCD screens of the same make and model. The grade is determined by the manufacturing quality control procedures.
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