[b]Are there any differences between the two technologies?[/b]
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?
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 tv screen comprises of millions of tiny ‘light bulbs’ which are small glass cells filled with inert gases such as xenon and neon. These cells are lit by a current being applied to electrodes in the gas filled cell and its atoms become ‘excited’ to a plasma and emit photons of ultraviolet light. These photons in turn hit a phosphor coating which emits visible light. The colour of the visible light emitted by each cell depends on the three different coloured phosphors - red, blue and green, and can together produce billions of colours when combined. As with the LCD tv screen, the millions of cells intermix to form the image on the screen. Currently the only manufacturers of Plasma tvs in the UK are Panasonic, Pioneer, Philips, LG, and Samsung. Plasma tvs are available in sizes from 32 inches to 150 inches.
[b]How does the Picture quality and the performance compare?[/b]
[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.
[b]The effect of the Contrast Ratio and the Black Levels.[/b]
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.
Colour Saturation
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.
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
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 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.
[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.
[b]Screen Image retention[/b]
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.
How does the Power consumption of LCD tv and Plasma tv compare ?
LCD tvs have a backlight that is continuously on and uses almost constant power. LCD tvs usually have an adjustable back light which uses extra power when it is on a high setting and a smaller amount on a low setting. The power necessary to alter the pixels is infinitesimal.
On a plasma tv the gas is charged in each of the pixels to emit light. When more light is in a scene the plasma tv uses more energy. When the brightness is high the plasma tv use more energy and when the brightness is low the plasma tv uses less energy. So the power consumption will vary depending on what is being displayed.
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
[b]Conclusion - which should you buy?[/b]
Both technologies have benefits. Plasmas tvs usually have a better subjective picture with better black level, higher contrast, and superior colour rendering than LCD TVs. Though LCD TVs have higher brightness, and no screen burn-in worries, and are lighter and thinner. This is not always the case becausea good LCD TV may have a better picture than an middling or poor plasma TV. Although 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 afford on you preferred format.
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