Flat Panel TV’s
After the invention of colour TVs in 1950s, the next best invention to capture the minds of people has been the Flat Panel TV technology. With the option to treat the Flat TVs as a part of the wall than as a part of the furniture, people have gone gaga over it.
The rage with which it is being sold, the CRT models may soon become antique pieces. But again there are many CRT loyalists who contend this, as there are many technical aspects where Flat TVs, Plasma or LCD, are yet to beat the old rival the CRT tube technology.
The conventional tube TVs have lost out due to the following reasons:
- They are heavy because of the sealed glass picture tube
- They have deep cabinet structure. Its long electron gun creates images by firing continuous beams of electrons, horizontally scanning the phosphor dot coated front panel.
- They are out of focus at the screen’s edges because of wider angle of firing. In spite of their excellent picture quality and affordable prices, they are getting replaced at a faster rate. Looks matter a lot!
In spite of their excellent picture quality and affordable prices, they are getting replaced at a faster rate. Looks matter a lot!
Working Principle
Understanding the basic working principle of the digital display technologies will help understand the following sections more easily. A digital image is produced by a rectangular array of picture elements (pels or pixels). Each pixel in the display panel is made of three sub-pixels for the three additive primary colours: red, green and blue. All shades of colours from bright white to pitch black are produced from the mixture of these colours. (Image from http://www.tomshardware.com/2005/03/09/lcd_or_plasma_/index.html)
Fig 1: Digital Image ComponentsPlasma display consists of two transparent glass panels sandwiching a thin layer of pixels. Each pixel is made of three gas filled cells. The gas used is a mixture of inert gases neon and xenon. A grid of tiny electrodes supplies electric current to these sub-pixels, as a result of which the gas ionizes to plasma state. Buyers need not worry about the leakage of this gas as they come in completely sealed units. This ionized gas emits high frequency UV rays, stimulating the cell’s phosphors to glow to the desired colour.
In a LCD display each pixel acts as a switch, they don’t emit any light. Instead there is a white back lighting. This light passes through the liquid crystal then through colour filter. The liquid crystal solution is trapped between two polarised glasses. Each sub-pixel is controlled electrically and thus more or less light is allowed to pass through the crystal, then through the polarised glass on to the display surface. Controlled red, green, and blue shades are thus emitted.
Digital Light Processing (DLP) TVs are the best technology for very large screens. Optical semiconductors are used. They are basically tiny mirrors that control the red, green, and blue sub-pixels on the screen. They don’t have the inherent burn-in disadvantage of Plasma technology or the lack of true blacks as in LCDs. The only disadvantage being they are not thin and you cannot hang on a wall.
Technology – LCD or Plasma
While pondering over which TV to buy, the first two basic factors to be considered are budget and screen size. Both are interrelated. Lower the budget, smaller will be the screen size. But if you are going out with a bulging pocket, the increased screen size will force you to consider which technology to opt for.
Physical Factors: For space efficiency, wall mounted flat TVs are ideal. Most flat panel TVs are four inches deep, some even lesser. Plasma TVs weigh more than LCD TVs, however both are lighter when compared with CRT models. Both plasma and LCD TVs are available in sizes ranging from 40inches to 65inches. Plasma employs gas Plasma technology, the screen turns hot and has in-built fans that can be noisy. This technology performs poorly at higher elevations and cold weather.
Some Plasma TV models:
Samsung – HPR6372 63inches Plasma HDTV
Price $7,000, Samsung HPR6372 63 Inch Plasma HDTV
Panasonic – 65PHD8UK 65inches Plasma HDTV
Price $8,400, TH-65PHD8UK 65″ Panasonic Plasma HDTV
Amazon – MU 60PZ95V 60inches Plasma HDTV
Price $7,300, MU 60PZ95V – 60″ HD plasma TV,
Plasma TVs have more options for larger screen sizes.
Some LCD TVs:
Sharp – LC-65D90U 65inches LCDHDTV
Price $20,000, Sharp LC-65D90U 65″ LCD HDTV
Samsung – LN-S5797 57 inches 1080p LCD HDTV
Price $10,000, Samsung LN-S5797 57″ 1080p LCD HDTV
In a large LCD display, there are chances that of all the switching transistors etched onto the surface of the display glass substrate; some may turn out to be defective. Not so the case with Plasma TV. Both are almost on par as far as size is considered, but for sizes >50inches, the plasma technology scores and at lower end of dimension <37inches the LCD technology is dominant.
For smaller, trimmer versions, 15 to 34 inches, LCD TVs are the only choice.
Samsung – LNS3251D 32inches LCD HDTV,Samsung LNS3251D 32″ Wide LCD HDTV
Sharp – LC-26D4U AQUOS 26inches HD LCD TV, Sharp LC-26D4U AQUOS 26″ HD LCD TV
A direct comparison between Panasonic 57inch Plasma and Samsung 57inch LCD HDTV will reveal that, Plasma costs almost 50% of the price tag of LCD. But both do not have the same specifications. LCD has a resolution of 1920 x 1080 pixels while Plasma has lower screen resolution of 1366 x 768 pixels. The high prices of LCD can thus be attributed to the expensive production processes involved in bringing out such a high resolution. Plasma production processes give a better yield compared to the number of discarded LCD panels due to bad pixels. Along with the high price tag, comes the no assurance tag from manufacturers that the LCD panel is free from bad pixels.
Now compare the 37inch TVs, prices are same for both Plasma and LCD. But LCD scores here for better picture details and screen resolution. Lowering the production costs can put LCD panels ahead in the race!
Presentation Factors
Consider these technical factors related to picture presentation on display panels: contrast ratio, black level performance, colour accuracy, viewing angle, supported picture detail. These factors too need to be kept in mind before one makes the final choice.
Black level performance: The picture quality depends on not only what is inside but also the exteriors, that is, the lighting. Under controlled lighting in the surroundings, Plasma provides better picture quality. As explained in the working principle of Plasma TVs, there is nil leakage of light between the adjacent gas cells. This property enables Plasma to display deeper blacks. This adds to picture depth, scene detail, and colour richness. All these features cumulatively provide a good picture contrast. In case of LCD, back light leaks through LCD layer, thus it is difficult to get true blacks. If darkness measured is expressed in figures, the darkest image on Plasma TV is a fraction of a Candela. While in a LCD the brightness is as high as two to three Candelas. This is when viewed from front, if viewed from an angle the image deteriorates further.
Plasma TVs provide more natural colouration as compared to LCD. The mechanism used in LCD is complex. White colour is filtered through micro filters built in sub-pixels; in this process the colour picture looses its accuracy and vibrancy. LCD panels are more suited to brightly lit rooms, as they employ anti-glare technology and have bright screen.
The LCD technology is improving at very fast rate. The latest models use intelligent backlight units that give improved colour freedom. The backlight unit uses LED and colour field sequential technology to eliminate the filters in sub-pixels. This enhances the colour detail of the picture.
The contrast ratio of LCD is many times lower than that of Plasma’s. Samsung’s LCD has a contrast ratio of 4000:1, while plasma has 10,000:1. The Plasma promoter may brag about this feature, but in reality, even in pitch darkness, the human eye is not able to perceive any difference in the contrast ratio in the range 4000:1 to 10,000:1. So this feature should hardly matter. Again, only when viewed at an angle, these features get reduced.
The Plasma scores in rooms with lower to normal lighting, while LCD overwhelms in brightly lit rooms!
Viewing Angle: The safest distance one can sit away from centre without experiencing any deterioration of picture quality is said to be the viewing angle. Plasma TVs have a better viewing angle than that of LCD’s. More than 1000 off axis, picture quality deteriorates as a result of colour shifts, reduced contrasts and loss of black level intensity. Samsung and Sony have lately come out with LCD TV sets that employ Super Patterned Vertical Alignment (S-PVA) technology. This has boosted viewing angles from 1700 to 1780 range. Viewing angle will soon cease to be an issue of concern.
Viewing Distance: Plasma technology gives a uniform image when the viewer is far from the panel. To display the image, the pixels are lit or unlit. For brightness the pixels are lit frequently, but for dark shades it is lit less often. The human eye undergoes tremendous strain viewing the flickering images at frequencies of 85Hz, without the viewer being even aware of it. LCD pixels don’t flicker. A safe viewing distance would be to maintain at least nine feet! For a shorter viewing distance smaller sized LCD panels will be a good choice but then keep in mind the black level performance.
Picture Resolution: For the same screen size LCD supports a higher resolution than Plasma’s. A 5o inch Plasma achieves the same screen resolution as that of a 4o inch LCD that is 1366×768 pixels. Thus for a bigger screen LCD requires more pixels, hence the panel costs more.
Factors related to functioning
Now consider these factors related to the functioning: burn-in, computer use, life-time, response time, bad pixels, and power requirements. These factors need to be evaluated before one can put the better technology to correct use.
Burn-in: The presence of a static image, mostly the logo of your favourite channel, for long durations can damage the phosphors in the pixel. The prematurely aged pixels in this area glow with lesser intensity than the surrounding pixels. Temporary burn-ins caused may wash-out after several hours of use and there are built-in features in some models which can remove the ghosts of the images left behind. Those that lead to permanent burn-ins, like the prolonged presentation of black or grey bars, are more worrisome. The permanently burnt pixels leave the ghost of your favourite sports channel logo even when you are watching a movie. Plasma panels also suffer from inconsistent fading out. With time, panels loose their brightness and that too not in an even manner. It is the blue channel which ages much faster.
Reduced burn-ins have been achieved to a certain extent with the use of better phosphor material and motion adaptive/pixel orbiting anti burn-in technology. Also a little care while viewing like lowering the brightness and contrast level can reduce the risk of burn-in. If TVs are to be rated purely on burn-in issue, then LCD scores. But for people with normal viewing habits Plasma can be a safe bet!
Computer use: LCD panel has more number of pixels per square inch when compared with Plasma’s. This factor enables display of larger amounts of data with exceptional clarity and precision. Thus the closer pixel built up structure and nil burn-in, as discussed earlier makes it a better choice for computer use and video games. Advantage LCD!
Life time: A 30,000 hours half life time would mean over 10 years of daily use before the flat panel TV sets would require replacement. Manufacturers of both technologies have come out with models which have a half life time of 50,000 to 60,000 hours. Compare this with 20,000 hours of half life time for CRT TV sets. Life time is no longer a serous issue to consider while buying a TV, people in US averagely change TV after every seven years due to advancement in performance and features. Both technologies are at par!
Bad pixel: Plasma rarely develops a bad pixel snag, but LCD may develop faulty pixels and sub-pixels with use. Before buying it will be wise to check the return policy, opt for a reputable brand. Most manufacturers are offering zero bad pixel policy. In this the TV is replaced within six months from the date of purchase, even if it develops a single bad pixel. Obviously Plasma scores!
Power Requirement: Plasma requires lighting up of each and every pixel of the display. The control lines of the electrode have to carry several hundred volts at high frequencies. This takes up substantial amount of power. LCD panels use a backlight to produce images and this requires much less power, about 40 to 50% less than that of Plasma displays. Another interesting comparison here is: Plasma requires more power to display bright picture while LCD requires more power to display dark picture. LCD‘s requirement will be for blocking more back light from reaching display surface!
The Final Word
Well, all these discussions cannot pinpoint to one single model being the ultimate choice. Developments are taking place at a very fast rate. The disadvantages today may no longer exist tomorrow. Prices will come down. What is not affordable today will be readily available tomorrow. A flat panel CRT offers better picture quality fewer problems, at much lesser price, but yes, they are bulky. Fashion buying is good but buyers must know what they are in for!
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