LCD and Plasma TV

LCD TV
Liquid crystal display television (LCD TV) is television that uses LCD technology for its visual output. The technology used is generally TFT. In the early 2000s, LCD flat-panels captured a large part of the computer monitor market from traditional CRTs. Continuing advances in LCD TV technology enable it to compete against Plasma flat panels and rear-projection televisions (DLP, LCD, and LCoS) for large-screen HDTV.

Early LCD television had drawbacks relative to traditional visual display technologies. It displayed fast-moving action with "ghosting" and could be viewed best only when looking directly at the screen or from a slight angle. These problems have largely been overcome in recent years, and LCD televisions, along with plasma displays, have taken over the dominant market position worldwide from cathode ray displays. The LCD design has the additional advantage of being more efficient in the use of electricity than the CRT design.

For a long time it was widely believed that LCD technology was suited only to smaller sized flat-panel televisions, and could not compete with plasma technology at sizes of 40" or larger. At the time, plasma held the edge in cost and performance. This belief has been undermined by the announcements of seventh-generation panels by major manufacturers such as Samsung, Sony, LG-Philips LCD, Westinghouse Digital, and Sharp Corporation:

* In October 2004, 40" to 45" televisions were widely available, and Sharp had announced the successful manufacture of a 65" panel.
* In March 2005, Samsung announced an 82" LCD panel.[1]
* In August 2006, LG.Philips Consumer Electronics announced a 100" LCD television [2]
* In January 2007, Sharp displayed a 108" LCD panel branded under the AQUOS brand name at CES in Las Vegas.[3]

Manufacturers have announced plans to invest billions of dollars in LCD production over the next few years, with televisions expected to be a key market. (The other main market for LCD displays is in computer monitors.)

Improvements in LCD technology have narrowed the technological gap with plasmas. The lower weight, falling prices, higher available resolution which is crucial for HDTV, and lower electrical power consumption of LCDs make them competitive against plasma displays in the television set market. As of late 2006, analysts note that LCDs are overtaking plasmas, particularly in the important 40" and above segment where plasma had enjoyed strong dominance a couple of years before. [4][5]

LCD screens produce very little glare from other light sources, as opposed to shiny plasma screens.

LCD Technology

LCD technology is based on the properties of polarized light. Two thin, polarized panels sandwich a thin liquid-crystal gel that is divided into individual pixels. An X/Y grid of wires allows each pixel in the array to be activated individually. When an LCD pixel darkens, it polarizes at 90 degrees to the polarizing screens.

This cross-polarizing blocks light from passing through the LCD screen where that pixel has darkened. The pixel darkens in proportion to the voltage applied to it: for a bright detail, a low voltage is applied to the pixel; for a dark shadow area, a higher voltage is applied. LCDs are not completely opaque to light, however; some light will always go through even the blackest LCD pixels.

Plasma TV

A plasma display panel (PDP) is a type of flat panel display now commonly used for large TV displays (typically above 37" or 940 mm). Many tiny cells located between two panels of glass hold an inert mixture of noble gases (neon and xenon). The gas in the cells is electrically turned into a plasma which then excites phosphors to emit light. It is often used in the home environment and is becoming increasingly popular in modern cultures.

Functional details

The xenon and neon gas in a plasma television is contained in hundreds of thousands of tiny cells positioned between two plates of glass. Long electrodes are also sandwiched between the glass plates, in front of and behind the cells. The address electrodes sit behind the cells, along the rear glass plate. The transparent display electrodes, which are surrounded by an insulating dielectric material and covered by a magnesium oxide protective layer, are mounted in front of the cell, along the front glass plate. Control circuitry charges the electrodes that cross paths at a cell, creating a voltage difference between front and back and causing the gas to ionize and form a plasma; as the gas ions rush to the electrodes and collide, photons are emitted.

In a monochrome plasma panel, the ionizing state can be maintained by applying a low-level voltage between all the horizontal and vertical electrodes - even after the ionizing voltage is removed. To erase a cell all voltage is removed from a pair of electrodes. This type of panel has inherent memory and does not use phosphors. A small amount of nitrogen is added to the neon to increase hysteresis.

In color panels, the back of each cell is coated with a phosphor. The ultraviolet photons emitted by the plasma excite these phosphors to give off colored light. The operation of each cell is thus comparable to that of a fluorescent lamp.

Every pixel is made up of three separate subpixel cells, each with different colored phosphors. One subpixel has a red light phosphor, one subpixel has a green light phosphor and one subpixel has a blue light phosphor. These colors blend together to create the overall color of the pixel, analogous to the "triad" of a shadow-mask CRT. By varying the pulses of current flowing through the different cells thousands of times per second, the control system can increase or decrease the intensity of each subpixel color to create billions of different combinations of red, green and blue. In this way, the control system can produce most of the visible colors. Plasma displays use the same phosphors as CRTs, which accounts for the extremely accurate color reproduction.

the article is taken from wikipedia.org