What is the difference between the flat screen technologies ?
Most people are not aware of the difference between LCD televisions, Plasma televisions and LED 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 is a size of Plasma tv that doesn't exist. What they actually mean is that it is a 26" LCD screen. So what are the differences between them and how do you spot them? All 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
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 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 the glass with a back light to show their colour as well as areas of light and dark. This is dependent 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 LED TVs Work
An LED Tv is an LCD Tv with a different type of backlight. An LCD tv takes its name from the type of panel used. An LED television takes its name from the type of backlight it uses. An LCD`s backlight is generated from slim fluorescent tubes which are situated horizontally at the rear of the television screen. An LED television either runs a length of LED lights across the frame of the tv which are then reflected through an LCD glass using mirrors (this is called Edge LED) or they are placed directly behind the screen in rows – this type is called Full LED. The reason why LED backlighting is used is that, firstly it produces a whiter light. This whiter light, due to its purity, allows a much better colouration to be produced and ultimately a wider colour spectrum. The second reason is that an LED is not as an intense light source and as such does not create as much light seepage ie light bleed as traditional LCD technology. The upshot of this is that you achieve less contamination of image, less “halo effect, and as such a better image. A further distinct advantage is that LED can be adjusted independently. Dynamic LED lighting allows the LEDs situated on the frame of the TV to be adjusted dependant on whether the image is light or dark, although this can be limited as if you have a widely contrasting scene then you have to rely on the LCD pixel to twist as well as traditional polarisation techniques to create black, which as we know is not ideal. The concept of Full LED allows a more precise way of controlling darkness and lightness as the LED is situated directly behind a cluster of pixels thus allowing a more focused and more precise way of controlling the dynamic contrast levels.
How does a Plasma screen display a picture?
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
LCD and LED TVs can be brighter than plasma TVs. This perception of brightness is of course reliant on where the TV is located and what is being watched. In reality all the technologies are capable of producing a level of that is well in excess of what is necessary in normal viewing.
Black Levels and the Contrast Ratio
The contrast ratio is a measure of the variation in light and dark tones that a panel can produce - in the main 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. New advances in technology such as LED backlighting have created techniques to thwart light leakage, and increase contrast ratios so that they are more comparable with Plasma tv, although still not quite 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. A Tv with the deepest blacks can be clearly seen to generate the richest colours and thus more realism. Devoid of deep black levels the colours can look more 'pastel' like. Typically the black on an LCD tv screen is more 'grey' when compared to the plasma tvs black. Although, if you look at a good quality LED tv and compare to a plasma, the divide has been narrowed substantially.
This is a gauge of the accuracy of the colours on the screen based on the presence 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 ability 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. A similar reasoning can be seen with LED tech too. Due to the nature of LED being less intense and more subtle, again, stray light has been reduced over that on traditional LCD tvs which gives a noticeably better and more vibrant image reaching that of plasma.
The Colour Gamut
Is the breadth and quantity of colours that can be displayed. The most costly models are now claiming to have colour gamuts which are near to full spectrum for plasma tv and LED tv. In fact most plasma TVs are simply a lot better than LCD tvs and it is only LED that can really compete with a top of the range plasma screen tv.
TV Screen Resolution
This can be defined as the amount of information shown on a screen. The more information that can be placed on screen the higher the quality of the image. A higher resolution usually means that the screen can display a higher quality image which has more detail and greater sharpness. The resolution is measured in pixels. LCD / LED HDTVs and Plasma HDTVs (High Definition Televisions) typically have a resolution of 1920 pixels x 1080 pixels or 1080P (Although some older models or smaller ranges have a resolution of 1366 x 768). The '1080' is the vertical resolution and 'P' denotes it is progressive scan meaning that the image isn't interlaced in nature. Usually LCD HDTVs are cheaper than the same sized Plasma's, although we are now seeing LED at a similar price to a top of the range Plasma screen. HD plasma are available in sizes of 42 inches upwards whereas LCD and LED HDTVs are available from 15 inches upwards.
Refresh Rate and Response Time of the screen
How a screen is able to deal with fast moving pictures without blurring is a combination of the refresh rate and 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 and ultimately refresh the image, a distinct blurring occurred which could be clearly seen. Recent improvements in screen technology has improved this response time to a point where it is no longer a major issue and has reduced dramatically motion blur. Now the cause is mainly the refresh rate or frame rate.
Lower end models of LCD televisions LED 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 now reduced dramatically with the addition of 100hz, 200Hz, 400Hz, 600Hz (and we are now seeing with a recent Philips screen 1200Hz) which creates extra frames that are placed between the normal frames. A normal signal is 50 Hz, with 100Hz 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. With 200Hz this introduces 3 additional frames which cycle the image at the equivalent of 200 frames per second and so on. The very best Plasma tvs still show fast moving images better than the best LCD tvs but the difference is narrowing and especially with LED tv, response times have been reduced dramatically to around 0.5ms on some of the very best on the market.
The Viewing Angle
Pictures on plasma TVs are however clearly viewable at about 160 degrees and on some models up to 180 degrees. With LED and LCD the picture can dull beyond about 100 degrees due to the nature of the construct of an LCD glass. In plane viewing panels have made things better, and the issue of an image “going off” at extreme angles is becoming less and less as developments take hold, although at the extreme an LCD does have a tendency to lose a little of its image ability.
The screen surface of lcd tvs and plasma tvs
LCD tv screens are available with matt finish screens which reduce glare whereas Plasma tvs have a reflective screen. There has been a tendency recently for LCD and more predominantly LED manufacturers to place a gloss look on the screen. This has meant that a distinct advantage over plasma has been lost by some LCD and LED tvs, purely to make the tv look more attractive. The issue of reflection, although has not gone away, has been managed by manufacturers adding clever anti reflective coatings the telly screen.
For Plasma Tvs, with prolonged displaying of non-moving images, graphics or text, such as a menu bar, channel logo, or news scrolling creates a permanent ghost image which 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. The problem of burn-in has been exaggerated over recent years and is very unlikely under normal viewing.
This is often confused with burn-in as it appears to be similar but the issue is not permanent. With this the 'ghost image' vanishes quickly with no lasting image burn occurring. For technical reasons image retention is normal and present on Plasma tvs but under normal viewing conditions hardly ever noticed at all. The effect was historically minimised by having a 'break-in' period for the first 100 hours of the plasma tvs life. During this period it was advised that you 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 reduce the brightness and contrast to a middle level and avoid dynamic or vivid factory settings on initial startup. Most Plazma televisions these days have circuits built in to them to greatly reduce the chance of either image retention or burn-in and as a whole is never really heard of these days.
How does the Power consumption of LCD tv and Plasma tv compare ?
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.
LED has taken this even further as the LED backlighting can be adjusted under normal working conditions dependant on the scene on screen. This greater efficiency in managing the power hungry backlighting means much lower power consumption and ultimately a more eco friendly flat screen experience.
Plasma tvs on the other hand charge a gas within the plasma screen to generate light. The more light that is required the more often this is done. So it's usual for plasma tvs to require more energy on an image with high levels of brightness, and less energy on low brightness scenes. So the power consumption varies.
The energy requirements that are quoted for Plasma tvs are for full brightness settings(as per EU law). The effect of this is that lcd tvs seem to use less power than plasma tvs. But the power consumption of a plasma tv varies depending on the amount of dark and bright areas on the displayed image. Studies have found that when the viewed programs are mainly dark the amount of power consumed on a plasma tv can be lower than an lcd tv. However when the viewed programs are sports and cartoons the power consumption for plasma tvs is greater than on lcd tvs. When varied programs are viewed the power consumption is similar for LCD tvs and Plasma tvs. Current plasma tvs now consume upto less than half the amount of power consumed a few years ago, although they are still going to have to try very hard to consume less energy than the ultra eco LED tv screens.
Plasma tv manufacturers are now quoting figures of 100,000 hours for the life expectancy. This represents a usage level of approximately 11.5 years of continuous use. So any concerns regarding the life expectancy of plasma tvs being less than LCD and LED tvs are completely unfounded.
Conclusion - which should you buy?
Lcd tvs, LED tvs and plasma tvs are able to offer pros and cons. An LED and LCD tv have higher brightness, have no chance of any screen burn and deal with brighter viewing environments better than a Plasma screen. They are also available in thinner / slimmer designs and they are lighter. When comparing picture quality, the plasma tv have more lifelike colours, have higher contrasts and blacks that are blacker and richer than lcd tvs. This is not necessarily the case for all plasma tvs compared to lcd tvs and especially LED tvs. A budget plasma tv will be out performed by a top of the range LED tv. On balance, when the pros and cons are considered, a plasma tv is still the one to choose, but like anything else spend as much as to can on the right one to get the very best image you can.
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