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What is the difference between the flat screen technologies ?

When it comes to flat screen TVs the two technologies LCD and Plasma appear very similar with almost lifelike images and the ability to be hung on the wall. Although LCD tvs and Plasma tvs panels may look very similar in the shops, there are lots of differences between the two technologies.

How does an LCD (Liquid Crystal Display) television work ?

The LCD tv screen is a thin flat display device and is made up of a two clear panels which have many colour liquid crystal filled pixels that are arranged in arrays in between them. When a small voltage is applied to the crystals they twist or untwist repositioning themselves so that light can either pass through or it is blocked. When millions of crystals do this a picture is displayed. Very little power is used in this process. Behind the screen is a back light that illuminates the pixels and displays a colour depending on their colour (either red, blue or green), also areas of light and dark spots are displayed depending on how they are positioned. LCD devices are available in small sizes for items such as a watch up to 108 inches. Most television manufacturers produce LCD television including Hitachi, JVC, LG, Panasonic, Pioneer, Philips, Samsung, Sharp, Sony, and Toshiba.

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.

A comparison of the Picture quality and Performance

Brightness

LCD TVs can be brighter than plasma TVs. This perception of this brightness is of course dependent 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 needed in normal viewing.

Black Levels and the Contrast Ratio

The contrast ratio is a measure of the difference in light and dark tones that a panel can produce - in general a high ratio means greater details can be discerned. Historically LCD tv panels have had a poorer contrast ratio than plasma tvs because the backlight bleeds through darkened pixels and lightens the image. Recent advances in technology have produced techniques to thwart 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 significant because black encompasses the entire spectrum of colour. And so, the deepest blacks generate the richest colours and hence more realism. Without 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.

Levels of Colour Saturation

This is a measure of the accuracyof 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 prevents the emission of stray light that diffuses colour. This is why tints and hues on Plasma TVs are noticeably more vivid and vibrant

[b]Colour Gamut level[/b]

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

How a screen is able to deal with fast moving pictures without blurring is a combination of the refresh rate and the response times. The response time is a measure of the speed of a screen to quickly change when an input signal is received. Early LCD tvs had a lot of motion blur caused by slow response times because the pixels took too long to change from on to on to off, and back on to on to refresh the image. Improvements in screen technology has improved this response time to the point where it is no longer the cause of the motion blur. Now the cause is mainly the refresh rate or 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

This is the maximum side angle that a viewer can see the image on the screen clearly. Plasma tvs usually have a viewing angle of between 160 degrees to 180 degrees whereas LCD tvs have a viewing angle of around 100 degrees after which the picture dulls.

The screen surface of lcd tvs and plasma tvs

LCD tv screens are available with matt finish screens which reduce glare but Plasma tvs have a reflective screen.

[b]Screen Burn-in[/b]

This can result if a static image is present on the screen for a prolonged time, and even after the image is altered or removed, the 'ghost image' of the formerly displayed static image is still noticeable on the screen for the remainder of the screens life. burn-in doesn't take place on LCD tvs. However the expose of burn-in on plasma tv is by and large exaggerated and improbable.

Image retention

Many people mix up burn-in with image retention which is very similar. With image retention the 'ghost image' disappears quickly either as soon as a new, bright image is displayed or after a few seconds. image retention is infrequently noticed but normal on plasma tvs because of the technology utilized, but it can be minimised by having a 'break-in' period when the plasma tv is first bought. The break-in period usually lasts 100 hours, during this time you should not view any programs that don't fill in the whole screen, and you shouldn'tview any programmingthat have static images such as bright station logos or news scrolls at the bottom of screens, and you should lower the contrast and brightness to a mid level. Nowadays there are also features built in to the plasma tvs to cut the chance of either burn-in or image retention.

[b]Is there any difference in power consumption of LCD tvs or Plasma tvs ?[/b]

LCD tvs have a backlight that is alwayson and uses almost constant power. LCD tvs usually have an adjustable back light which uses more power when it is on a high setting and less on a low setting. The power required to alter the pixels is infinitesimal.

But Plasma tvs charge a gas to a plasma to produce light. The more light that is necessary the more often this is done. So it's normal for plasma tvs to need more energy on an image with high levels of brightness, and less energy on low brightness scenes. Therefore the power consumption varies.

On paper it might seem that the Plasma tvs use a lot more power than LCD tvs. Plasma tv manufacturers have a tendency to quote the highest power usage at full brightness. Although the plasma tvs power power consumption changes depending on the signal and the amount dark and bright areas on the screen. Studies have shown that when viewing predominantly dark programs and movies the average power power consumption of an equal sized plasma tv is actually lower than LCD tv. On the other hand if lots of cartoons and sport are watched then the LCD tv consumes less power. So on average with varied viewing content there is little difference between LCD tvs and Plasma tvs. Plasma tv manufacturers are shortly going to be launching models that will cut the power consumption by over half.

Life expectancy of Plasma televisions

Many 'experts' claim that plasma tvs don't last very long. But in reality manufactures are publishing life expectancy figures of 100000 hours, this equates to 11.5 years of non stop use. Clearly there is no reason for concern.

Conclusion - which is the best?

Both lcd tvs and plasma tvs are able to offer pros and cons. The lcd tvs have higher brightness and no chance of any screen burn. They are also available in thinner designs and they are lighter. When comparing picture quality the plasma tv have more life like colours, higher contrast and blacks that are blacker than lcd tvs. This is not necessarily the case for all plasma tvs compared to lcd tvs. A budget plasma tv will be out performed by a top of the range LCD tv. On balance when the pros and cons are considered a plasma tv is the obvious choice but spend as much as to can on one.