LCD television or Plasma television – which one ?
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What is the difference between the flat screen technologies ?
Most people are not aware of the difference between LCD televisions and Plasma televisions. Quite often people will refer to a flat panel tv as a Plasma tv or an LCD tv incorrectly as a generic term. e.g. a 26 inch Plasma tv, a size of Plasma tv that doesn’t exist. What they actually mean is a 26″ LCD screen. So what are the differences between them and how do you spot them? Both flat panel technologies can be hung on the wall and can produce unbelievably realistic images that make you feel that you are there.
How LCD tvs 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 plasma tvs works
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
[b]The Brightness of the picture[/b]
LCD tv screens are able to produce a brighter picture than a Plasma screen. How noticeable or useable this difference is will depend on the location of the screen and what is being viewed. But in normal viewing conditions both LCD televisions and Plasma televisions are able to produce more than enough picture brightness.
[b]The effect of the Contrast Ratio and the Black Levels.[/b]
This is a measure of the difference of the luminosity of the brightest white on the screen and the darkest black. So a contrast ratio of 3000:1 means that the brightest white is 3000x brighter than the darkest black. Details can be more easily differentiated the higher the contrast ratio is as long as the the black levels aren’t ‘grey’. Previous models of LCD tvs had lower contrast ratio than plasma tvs because the pixels weren’t able to block the back light for dark areas and the light would leak through making the image lighter. Improvements in technology have reduced this leakage so that the contrast ratio is much closer to those of plama tvs. But ultimately plasmas are able to produce blacker blacks because the pixel cells are able to be switched off instead of blocking the light as lcd tvs do. The blacker the black on a tv the better the picture quality it is able to produce. The colour saturation or colour palette is affected if the blacks aren’t black enough . When the black level on a plasma is compared with the black level on an comparable priced LCD tv, the plasma tv black often makes the LCD tv black look grey.
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.
Colour Gamut
Is the range and quantity of colours that can be displayed. The most costly models are now claiming to have colour gamut’s getting quite close to the full spectrum for plasma tv and LCD tv. In fact most plasma TVs have a propensity to be better than most LCD tvs apart from the top of the range ones. With the cheapest LCD tv models usually offering a colour gamut that isn’t as good the higher LCD tv models. So by and large the plasma tv has the best colour gamut.
TV Screen Resolution
This is the quantity of pixels that make up the screen. The higher the resolution is, the higher the definition and the sharper picture is. Presently, LCD HDTV’s generate the image at 1920 pixels x 1080 pixels, full 1080p resolution at a lesser cost than plasma tv panels of the same size. There is no difference in an HD LCD tv or Plasma tv for screen sizes above 37 inches. However plasma tv screens of 37 inches and below are currently only HD Ready but LCD tv models are available from 32 inches upwards in full HD or 1080P.
Refresh Rate and Response Time
These two attributes in combination determine how fast a moving picture a screen can reproduces without the image blurring. Response time is a gauge of how rapidly 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 mostly caused by the refresh rate, or the frame rate.
All LCD tvs and Plasma tvs have until a short time ago had frame rates of 50 frames per second or 50hz. The more costly LCD tv and Plasma tv models now have 100 Hz to compensate for any motion blur. Since the standardsignal is only 50 Hz the added frames are fashioned with signal processing software which interpolates what the add-on middle frames should look like. The end result is moving pictures that loose hardly any definition and are more fluid. The best Plasma tv screens nevertheless respond better to fast motion than LCD tv but the difference has narrowed as the best LCD tvs motion response time has improved and 100hz and 200hz has been introduced.
The 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
LCD tv screens are available with matt finish screens which reduce glare but Plasma tvs have a reflective screen.
Image Burn-in
This is characterised by a ‘ghost image’ of a previously displayed static image that had been displayed for a prolonged period of time and is still present. Even if the screens image is changed from the original ‘ghost image’ or removed it is present for the rest of the plasma tvs life. For LCD tv screens burn-in isn’t a problem no matter how long the static image is displayed. Nonetheless the burn-in risk is overstated and improbable in normal viewing conditions.
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.
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.
On paper it may seem that the Plasma tvs employ a lot more power than LCD tvs. Plasma tv manufacturers tend to quote the most 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 lessen 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.
[b]Conclusion – which should you buy?[/b]
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.
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