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					LCD Television

Liquid-colour display televisions (LCD TV) are television sets that use LCD
technology to produce images. Benefits of LCD technology include lower
weight and reduced power requirements when compared to other display
types. Often, LCD television screens can also be used as computer monitors.

LCD Technology

The pictures on a CRT TV / Monitor do not exhibit any sort of "ghosting,"
because the CRT's phosphor, charged by the strike of electrons, emits most
of the light in a very short time, under 1 ms, compared with the refresh period
of e.g. 20 ms (for 50 frame/s video). In LCDs, each pixel emits light of set
intensity for a full period of 20 ms (in this example), plus the time it takes for it
to switch to the next state, typically 12 to 25 ms.

The second time (called the "response time") can be shortened by the panel
design (for black-to-white transitions), and by using the technique called
overdriving (for black-to-grey and grey-to-grey transitions); however this only
can go down to as short as the refresh period.

Video material, shot at 50 or 60 frames a second, actually tries to capture the
motion. When the eye of a viewer tracks a moving object in video, it doesn't
jump to its next predicted position on the screen with every refresh cycle, but
it moves smoothly; thus the TV must display the moving object in "correct"
places for as long as possible, and erase it from outdated places as quickly as
possible. LCD televisions are also a good component for video games.
Although ghosting was a problem when LCD TVs were newer, the
manufacturers have been able to shorten response time to 2ms on many
computer monitors and around an average of 8 ms for TVs.

There are two emerging techniques to solve this problem. First, the backlight
of the LCD panel may be fired during a shorter period of time than the refresh
period, preferably as short as possible, and preferably when the pixel has
already settled to the intended brightness. This technique resurrects the
flicker problem of the CRTs, because the eye is able to sense flicker at the
Another approach is to double the refresh rate of the LCD panel, and
reconstruct the intermediate frames using various motion compensation
techniques, extensively tested on high-end "100 Hz" CRT televisions in
Europe.

LCD technology is based on manipulation of polarized light. Two thin
polarizing sheets are laminated to two glass substrates containing a thin layer
of liquid-crystal. A regular 2-dimensional grid of electrodes allows each pixel
in the array to be selected and activated individually. Several LCD
technologies are used for the realization of large format television screens
(e.g. TN, IPS, PVA, FFS), all in combination with active-matrix addressing.
It had been widely believed that LCD technology was suited only to smaller
sized flat-panel televisions at sizes of 40" or smaller. Early LCDs could not
compete with plasma technology for screens larger than this because plasma
held the edge in cost and performance. However, LCD TVs can now offer
acceptable performance in larger sizes.

Developments in LCD televisions

Current sixth-generation panels by major manufacturers such as Samsung,
Sony, LG Display, and the Sharp Corporation have announced larger sized
models:

In October 2004, 40" to 45" televisions became 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 Display 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]

In November 2008, Silicon Mountain announced Allio, a 42" High-Definition
LCD TV with an integrated Blu-ray player and full function media center PC.[4]

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.

Improvements in LCD technology have narrowed the technological gap,
allowing producers to offer lower weight and higher available resolution
(crucial for HDTV), and lower power consumption. LCD TVs are now more
competitive against plasma displays in the television set market. It is noted
that LCDs are now overtaking plasmas, particularly in the important 40" and
above segment where plasma had enjoyed strong dominance.[5][6] TVs
based on PVA and S-PVA LCD panels deliver a broad viewing angle, up to
178 degrees.[7] They also deliver an adequate contrast ratio for viewing bright
scenes, as well as dark scenes in bright rooms. The dynamic contrast
technique improves contrast when viewing dark scenes in a dark room.
Alternatively, some manufacturers produce LCD TVs that throw light on the
wall behind it to help make dark scenes look darker. PVA and S-PVA panels
generally have difficulty with ghosting when going between different shades of
dark colors, however in new televisions this is compensated to some degree
using a technique called overdriving.

DVD players are commonly integrated into LCD TVs. Currently, Sharp, and
Silicon Mountain are selling LCD TVs with integrated Blu-ray Disc players.
Sharp is also promising to sell LCDs with built-in Blu-ray Disc recorders by the
end of 2009.

Recent research
Some manufacturers are also experimenting with extending color
reproduction of LCD televisions. Although current tft panels are able to deliver
all sRGB colors using an appropriate combination of backlight's spectrum and
optical filters, manufacturers want to display even more colors. One of the
approaches is to use a fourth, or even fifth and sixth color in the optical color
filter array. Another approach is to use two sets of suitably narrowband
backlights (e.g. LEDs), with slightly differing colors, in combination with
broadband optical filters in the panel, and alternating backlights each
consecutive frame.

Otherwise, the only use of the extra colors would be to let the looker boost the
color saturation of the TV picture beyond what was intended by the producer,
but avoiding the otherwise unavoidable loss of detail ("burnout") in saturated
areas.

References

   1.   ^ SAMSUNG United States - Main
   2.   ^ About Philips - Royal Philips
   3.   ^ FOXNews.com - Sharp Unveils 108-Inch Flat-Panel TV - Science News | Science &
        Technology | Technology News
   4.   ^ Tom's Hardware Silicon Mountain Unveils Allio All-in-One HTPC TV
   5.   ^ http://news.zdnet.com/2100-9584_22-6138290.html
   6.   ^ Shift to large LCD TVs over plasma - HDTV - MSNBC.com
   7.   ^ ::: Hyundai IT :::

				
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posted:3/14/2010
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