From Simple English Wikipedia, the free encyclopedia
LCD television
Aliquid crystal display is a special thin flat panel that can let light go through it, or can block the light. (Unlike anLED it does not produce its own light). The panel is made up of several blocks, and each block can be in any shape. Each block is filled withliquid crystals that can be made clear or solid, by changing the electric current to that block. Liquid crystal displays are often abbreviatedLCDs.
Liquid crystal displays are often used inbattery-powered devices, such as digital watches, because they use very littleelectricity. They are also used for flat screenTV's. Many LCDs work well by themselves when there is other light around (like in a lit room, or outside in daylight). Forsmartphones,computer monitor, TV's and some other purposes, a back-light is built into the product. This is an LED orCold Cathode Fluorescent Light (CCFL).
The LCD uses technology calledelectro-optical modulation. This means it uses electricity to change how much light passes through it.
Each pixel (block) of an LCD is made of a thin layer ofmolecules between twoelectrodes and twopolarizingfilters. The electrodes provide electric power to the liquid crystal layer, and don't block the light. Light travels with 'polarity' or direction, and a polarizing filter only lets light with one kind of polarity to go through it, like trying to slide a ruler through a narrow opening. Only when the ruler is lined up right, will it fit. These two filters areperpendicular to one another, so the narrow openings are in different directions. This means that without the liquid crystals between them, they would block all light from passing through – whatever light gets through the first filter will not fit through the second filter.
LCD with top polarizer removed from device and placed on top, such that the top and bottom polarizers are parallel
The layer of liquid crystals between the two filters can 'twist' the light so that the polarity changes. This means the light can then pass through both filters, and the pixel appears clear. When giving an electric current to the liquid crystals, the molecules will untwist and will not change the light. The filters then block the light and the pixel appears dark.[1]
The chemical formula of the liquid crystals used in LCDs may vary. Formulas may be patented.[2] An example is a mixture of 2-(4-alkoxyphenyl)-5-alkylpyrimidine with cyanobiphenyl, patented by Merck andSharp Corporation. The patent that covered that specific mixture expired.[3]
When a large number of pixels are needed in a display, it becomes difficult to have enough wires and electrodes to control each pixel and still have a clean display. Instead, the display ismultiplexed. In a multiplexed display, electrodes on one side of the display are grouped and wired together (usually in columns). On the other side, the electrodes are also grouped (typically in rows), with each group getting a voltage sink. By turning on one row and one column, each pixel can be controlled one at a time.
