by Armadeus Cornelius
What is the difference between the flat screen technologies ?
When it comes to flat screen TVs the two technologies LCD and Plasma look very alike with almost lifelike images and the ability to be hung on the wall. Although LCD tvs and Plasma tvs displays may look very similar in the shops, there are many differences between the two technologies.
How does an LCD (Liquid Crystal Display) television work ?
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.
[b]How does a Plasma screen display a picture?[/b]
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
Screen Brightness
LCD TVs can be brighter than plasma TVs. This perception of this brightness is of course reliant on where the TV is situated and what is being watched. In reality both technologies are capable of producing a level of brightness that is in excess of what is necessary in normal viewing.
Contrast Ratio and Black Levels
The contrast ratio is a measure of the difference in light and dark tones that a panel can deliver - generally a high ratio means greater details can be discerned. Historically LCD tv panels have had a lower contrast ratio than plasma tvs because the backlight bleeds through darkened pixels and lightens the image. New advances in technology have created techniques to prevent light leakage, and increasecontrast ratios so that they are more comparable with Plasma tv, but still not as good. Because each cell on a plasma tv is able to be switched off rather than blocking the light as per LCD tvs the blacks are blacker. For a television picture, the black level is very important because black encompasses the entire spectrum of colour. And so, the deepest blacks produce the richest colours and therefore more realism. Devoid of deep black levels the colours look more ‘pastel’ like. Typically the black on an LCD tv screen is more ‘grey’ when compared to the plasma tvs black.
[b]Colour Saturation Levels[/b]
colour saturation is a measure, in the presence of grey shades, of colour purity or how accurate the colours are on the screen. The higher the colour saturation the more accurate the colour rendition. With blacks that aren’t as black the grey shades will be higher resulting in a lower colour saturation. Plasma offer better levels of colour saturation due to better black levels because of their ability to switch of pixels that aren’t in use, preventing diffusion of colours by stray light emissions. This results in hues and tints that are more life like colourful.
Colour Gamut
The colour gamut is a measure of the number of colours that a screen can display. For the most expensive models of LCD tvs and Plasmas tvs the manufacturers are now claiming to have colour gamuts very close to the full spectrum. Again on a like for like basis the Plasma tvs still out perform the LCD tvs on all but the most expensive models. This is because on cheaper LCD tv models the colour gamut isn’t as good as the top LCD tv models from the same manufacturer. Whereas for Plasma tvs the difference isn’t as great.
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.
Refresh Rate and Response Time
These two attributes in combination influence how fast a moving picture a screen can reproduces without the image blurring. Response time is a gauge of how quickly a screen can change 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 by and large caused by the refresh rate, or the frame rate.
Less expensive models of Plasma televisions and LCD televisions operate at frame rates of 50 frames per second or 50hz. Recently 100hz tv models were launched on more expensive models which reduced motion blur by creating an extra middle frame which is placed in between the normal frames. This middle frame is created by advanced signal processing software that interpolates what the middle frame would look like. The addition of the middle frame results in moving images that are fluid with little, if any definition loss. Even with 100hz the best plasma tvs still out perform the best LCD tv models but by a narrowing margin because of reduced response times and 100hz and 200hz.
Viewing Angle
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.
The surface of the screen
A plasma tvs screen is a shinny reflective surface which can suffer from glare depending on the room conditions, whereas LCD tv screens have matt finish that reduces glare.
Burn-in
This can result if a static image is present on the screen for an extended time, and even once the image is altered or removed, the ‘ghost image’ of the formerly displayed static image is still detectable on the screen for the remainder of the screens life. burn-in doesn’t happen on LCD tvs. But the probability of burn-in on plasma tv is usually exaggerated and not likely.
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.
Power consumption
The power consumption of an LCD tv is virtually constant because they have a back light that is on all of the time. The back light can be manually adjusted but uses less power on a low setting and more power on a high setting. The modulation of the LCD tvs screen pixels takes very little 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.
[b]Plasma tv Life expectancy[/b]
Plasma tv manufacturers are nowquoting figures of 100000 hours for the life expectancy. This represents a running level of almost 11.5 years of continuous use. So any concerns in relation to the life expectancy of plasma tvs being less than LCD tvs are unfounded.
Conclusion - which is the best?
Plasma televisions and LCD televisions both have advantages and disadvantages. LCD tvs have higher brightness, no concerns about screen burn, and they are thinner and lighter. But Plasma tvs have a better real world picture with a higher contrast, blacker blacks, and more natural colours than LCD tvs. Obviously not all Plasma tvs are better than all LCD tvs. A top specification LCD tv will out perform a cheap plasma tv. If you weigh up the advantages and disadvantages a good plasma tv is the best option but you do get what you pay for.