The LCD manufactures had made lot of innovations in the manufacturing of a lCD TV. Currently different types liquid crystals like dual super twisted nematics (STN), dual scan twisted nematics (DSTN), ferroelectric liquid crystal (FLC) and surface stabilized ferroelectric liquid crystal (SSFLC) are used. In addition, latest LCD TVs started using special plastic in place of glass making the TV lighter and flexible.
Backlight system
As back light of LCD TV is one of the most important determiners of the picture quality of LCD TV, developments are constantly happening in this area with each manufacturing coming with new backlight technologies.
With regard to backlight source , the following techniques are employed by the LCD makers.
1. Manipulating backlight device
By controlling the brightness of florescent lamps that make up the backlight source.
This technique produces fast movements on the screen with smoothness and realism . The brightness of backlight is controlled in synchronization with the picture source to enhance black depth and picture details.
2. Using alternative back light sources:
FFL backlight
LCD TVs generally use cold cathode fluorescent tubular lights (CCFL). Some new LCD TVs, as manufactured by Samsung employ the use of a flat fluorescent lamp (FFL) which offers thin design combined with uniform scattering of light on the screen. This new technology also provides improved brightness and contrast of the image.
Some LCD manufacturers use their unique florescent backlight by improving the existing CCFL in their LCD panels. The conventionally used CCFL is usually made up of three colours – red, green and the blue. However, the leading LCD make Sharp has come with its new 4-colour florescent backlight which adds fourth colour. Adding the fourth colour also known as red emitter, 4-colour florescent backlight enhances the colour clarity showing different red shades. There is also a LED absed backlight technology which can give better colour quality than 4-color florescent backlight. However, cost wise 4-color florescent backlight is much cheaper
LED based backlight
The backlight technologies based on LED, though costlier, are employed in some newer LCD TVs as they have certain advantages over the CCFL backlight technology.
LED based backlight device presents colours with unrivalled naturalness and true-to-life quality that cannot be expected from LCDs that standard CCFL backlight. This is because, the colours in LED based TVs are created based on the frequency or wave length of light. As a result, colours look more precise and resemble the natural hues. It has following advantages:
- The overall picture quality is much better in LCDs which use LED based backlight technology.
- LCD TVs which are based on LED backlight sources usually consume less electricity.
- LED based backlight sources have better longevity and can last three times longer than normal CCFL backlight.
Color Field Sequential Technology
Colour filters are generally used to produce a gamut of colours in a LCD display and they weigh about one-fourths of a LCD TV. The newer LCD TVs have found a way to replace colour filters using a method called Colour Sequential. This new technology allows the backlight device to discharge only one colour at a time, so in a sequence of three colours (RGB) each colour is displayed one after another. The colour sequential component and the backlight source work together to produce improved colour spectrum thus the colours look more crisp and richer.
Colour filters also suck up nearly three-fourths of light provided by backlight source. So, the use of colour filiters not only involves higher power consumption but will also lead to the short life of backlight. As the colour sequential system does not require colour filters, the power consumption is reduced to minimum. The display is much brighter while using the same amount of electricity.When colour filters are removed, it also makes a LCD lighter by nearly 25 percent.
Since, only one colour is displayed at a quick succession, each sub-pixel almost functions like an individual pixel. While this makes the screen to have three times more resolution than the normal screen, this technology also keeps the number of bad pixels to a bare minimum. The Sequential colour system changes the colours so rapidly that all the three colours produce a full-colour image which looks richer and better colour detailed.
Optically Compensated Bend (OCB)
A few LCD makers like Toshiba are well known for their small LCD panels and they have been using Optically Compensated Bend (OCB) liquid crystals to eliminate of problem of narrow viewing angles. Narrow viewing angles make the viewer to sit within the supported field of view to get the acceptable picture quality and the image usually gets deteriorated when seen from off-axis. But OCB enables the LCDs to have viewings angles more than 170 degrees.
These liquid crystals twist and untwist at much faster speed, so the response time is also greatly improved up to 3 ms while the standard response times is 8 ms.
Another drawback of LCD is also overcome by using OCB. They can withstand extreme temperatures especially cold temperatures, so LCDs perform better in such conditions.(sub zero temperatures).
