What is the difference between the flat screen technologies ?
Both LCD tvs and Plasma tvs appear to give similar levels of performance. So is there any real difference? Both are slim and can be hung on the wall. Many people will incorrectly refer to small screens as plasma tvs when they are LCD tvs. However both technologies work and perform very differently. What is the difference between the two technologies?
[b]LCD screens explained[/b]
LCD is an abbreviation for Liquid Crystal Display. A LCD tv screen is made up of two clear panels between which is a matrix of colour liquid filled pixels. These pixels respond to a small voltage which makes them change state by twisting or untwisting which allows light to pass through them or to be blocked depending on the state of the pixel. This process of twisting takes very little power. The pixels are either red, green or blue and they are structured in a matrix of millions of pixels to make a picture. The coloured pixels of the panel are illuminated from Behind with a back light to show their colour, and areas of light and dark, depending on how the pixels are twisted. Lcd screens are available in small sizes for watches up to 108 inches for large televisions. Manufacturers such as LG, Samsung, Hitachi, Panasonic, JVC, Pioneer, Sharp, Toshiba, Philips and Sony have a range of lcd televisions available.
How does a Plasma television work ?
A plasma panel consists of millions of minuscule phosphor coated, gas filled cells or pixels with electrodes in them. Inert gases such as Xenon and neon fill the cells. When a current is applied to the electrodes in the cells it charges up the gas with positive and negative ions. As the ions become excited they collide with each other producing photons of ultraviolet light which react with the coloured phosphor coating in the pixels releasing red, blue or green light. When these colours are combined it is possible to create billions of colours. A panel consists of millions of pixels which together create the picture. The only manufacturers of Plasma televisions are LG, Panasonic, Philips, Pioneer, and Samsung who produce sizes of 32 inches up to 150 inches.
Performance and Picture quality compared
[b]The Brightness of the picture[/b]
The picture on LCD tv screens can be brighter than Plasma tvs. Depending on where the television is located and what is being viewed will determine how this difference in
screen brightness is perceived. However both Plasma tv and LCD tv screens are capable of producing
brightness levels that in normal viewing conditions are in excess of what is needed.
Black Levels and the Contrast Ratio
The difference between the extreme of light and dark tones is known as the
contrast ratio. Usually the greater the contrast ratio is the more details can be differentiated. In the past LCD tv screens were known to have lower
contrast ratios than plasma tvs due to the pixels not being able to totally block the back light on darkened pixels and light would bleed through and make the image lighter. New methods of reducing this light leakage have been introduced on the latest LCD tv screens so that the
contrast ratios are closer to those of a Plasma tv. However Plasma tvs are still better because their pixel cells can be switched off, rather than blocking the back light with LCD tvs, and blacks are blacker. The
black levels on a television underpins the overall picture quality. If the blacks aren't black enough then the whole colour palette or
colour saturation is affected so that the colours appear artificial rather than life like. The
black level on an LCD tv is more dark grey when compared with the
black level on a plasma tv.
Levels of Colour Saturation
This is a measure of the correctness of the colours on the screen based on the existence of grey shades - the higher grey shades results in lower
colour saturation. Plasma TVs have high
colour saturation due to the way they emit light. The capability of Plasma tv pixels to be switched off when they are not in use stops the emission of stray light that diffuses colour. This is why tints and hues on Plasma TVs are noticeably more vivid and vibrant
The Colour Gamut
The
colour gamut is the set of possible coulors within a colour spectrum that a screen can display. The top end models of Plasma tv and LCD tv manufacturers are claiming that the
colour gamut is near to the full spectrum. On comparable priced LCD tv and Plasma tvs, the Plasma tv again out performs the LCD tv on all but the top end models. The reason for this is that for the same manufacturers the
colour gamut isnt as good on the lower models. On plasma tv models the cheaper models don't have such a difference compared to more expensive models from the same manufacturer.
Resolution
This can be defined as the amount of information shown on a screen. The more information that is on a screen the higher the quality of the image. The higher resolution usually means that the screen can display a higher quality image with more detail and sharpness. The
resolution is measure in pixels. LCD HDTVs and Plasma HDTVs (High Definition Televisions) have a
resolution of 1920 pixels x 1080 pixels or 1080P. Where '1080' is the vertical resolution and 'P' is progressive scan meaning that the image isn't interlaced. Usually LCD HDTVs are cheaper than the same sized Plasma's. HD plasma are available in sizes of 42 inches upwards whereas LCD HDTVs are available from 32 inches upwards. Therefore at sizes 32 inches to 37 inches LCD tvs have the advantage of offering 1080P HD compared to the 720P (1280 pixels x720 pixels) HD Ready Plasma tvs. At sizes less than 32 inches there aren't any plasma tv models.
Response Time and Refresh Rate
These two attributes in combination establish how fast a moving picture a screen can reproduces without the image blurring.
Response time is a measure of how fast a screen can vary when an input is received. Historically LCD tv panels had slow
response times which was the limiting factor causing motion blur because each pixel has to go from an on state, to an off state, and back to on in order to
refresh an image. Improvements in pixel
response times on LCD tv screens means that the actual
response time isn't the main cause of motion blur, its generally caused by the
refresh rate, or the frame rate.
Lower model of LCD televisions and Plasma televisions operate at a frame rate of 50hz or 50 frames per second. In fact until recently, before 100hz models were launched, all models operated at 50 Hz. Now on more expensive models of LCD tv and Plasma tv motion blur is reduced with the addition of 100hz which create an extra frame that is placed between the normal frames. Because a normal signal is 50 Hz an additional middle frames is created by signal processing software that interpolates what the extra middle frame should look like. This results in picture motion that is more fluid and looses little if any definition. However the best Plasma tvs still show fast moving images better than the best LCD tvs but the difference is narrowing because the LCD tvs
response time has reduced and 100hz and 200hz models have been established.
[b]The Viewing Angle of the screen[/b]
Pictures on plasma TVs are still clearly viewable at about 160 degrees and on some models up to 180 degrees. But the picture dulls further than about 100 degrees.
[b]The screen surface[/b]
Plasma tvs have reflective shinny screen surface which can be affected by glare depending on the viewing conditions. Lcd tvs have a matt finish which reduces glare.
[b]Screen Burn-in[/b]
For Plasma tvs With prolonged displaying of non-moving images, graphics or text, such as a menu bar, channel logo, or news scroll a permanent ghost image can be permanently burned on the screen with a darkened appearance. SO even if the image on the screen is changed or removed it can't be removed for the rest of the plasma tvs life and is always seen as a shadow image. Regardless of how long a static image is displayed on an LCD tv they aren't affected by
burn-in. But the problem of
burn-in is exaggerated and unlikely under normal viewing.
Image retention
This is often confused with
burn-in which appears to be similar but it isn't permanent. The 'ghost images' vanish quickly with
image retention when a new bright image appears or after a few seconds. For technical reasons
image retention is normal and present on Plasma tvs but hardly ever noticed. This effect can be minimised by having a 'break-in' period for the first 100 hours of the plasma tvs life. During this period you should watch programs that fill the whole screen and don't have any bright static images such as station logos or news scrolls at the bottom of the screen. You should also reduce the
brightness and contrast to a middle level. The latest Plasma televisions have circuits built in to them to greatly reduce the chance of either
image retention or
burn-in.
[b]Is there any difference in power consumption of LCD tvs or Plasma tvs ?[/b]
The backlight on an LCD tv is constantly on so the
power consumption is almost constant. By manually adjusting the
brightness of the back light up or down the
power consumption is either increased or decreased. The twisting and untwisting of the LCD pixels consumes hardly any power.
Because Plasma TVs charge the gas in the individual pixels to a plasma to create the light, and the more light that is required on a scene the more energy is used. So pictures with low
brightness in them use less energy, and high
brightness more energy i.e. the power consumption varies.
Quoted figures for Plasma television will quote maximum power consumption at maximum
brightness which may make it appear as if LCD tvs use a lot less power than them. But the power consumption of a plasma tv varies, according to the image displayed and the amount of bright and dark areas on the screen. Research has showed that a plasma tv displaying programs that are predominantly dark or movies will have a lower
power consumption than an LCD television. But if the programs watched are cartoons or sports then the
power consumption will be higher than an LCD television. If a mixture of different types of programs are viewed then there is little difference in the
power consumption between Plasma tv and LCD tv. The next generation of Plasma televisions will be reducing the
power consumption by in excess of half.
Life expectancy of Plasma televisions
It is common myth that is quoted that plasma tv screens don't last very long. However manufacturers such as Panasonic are quoting a
life expectancy of 100000 hours which is 11.5 years of continuous use. Therefore any concerns are unsubstantiated
Conclusion
Both technologies have advantages. Plasmas tvs usually have a better subjective picture with better
black level, higher contrast, and superior colour rendering than LCD TVs. Although LCD TVs have higher
brightness, freedom from screen
burn-in worries, and are lighter and thinner. This is not always the case sincea good LCD TV may have a better picture than an middling or poor plasma TV. But on balance I consider that a plasma tv is the better option with added advantages. In the end you get what you pay for so spend as much as you can manage to pay for on you preferred format.
Article Source: http://www.alltopinfo.com
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