Plasma vs LCD

Plasma vs LCD

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

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.

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

Screen Brightness

LCD TVs can be brighter than plasma TVs. This perception of this brightness is of course reliant on where the TV is located 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.

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 have created techniques to thwart light leakage, and increase contrast 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 generate the richest colours and thus 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.

Colour Saturation

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.

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 getting rather close to the full spectrum for plasma tv and LCD tv. In fact most plasma TVs tend to be better than most LCD tvs apart from the top of the range ones. With the cheapest LCD tv models more often than not 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 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 measured 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 of the screen

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.

Lower model of LCD televisions 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 reduced with the addition of 100hz which create an extra frame that is placed between the normal frames. Because a normal signal is 50 Hz 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. However the best Plasma tvs still show fast moving images better than the best LCD tvs but the difference is narrowing because the LCD tvs response time has reduced and 100hz and 200hz models have been established.

The Viewing Angle

Pictures on plasma TVs are however clearly viewable at about 160 degrees and on some models up to 180 degrees. But the picture dulls beyond about 100 degrees.

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.

Screen Burn-in

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.

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.

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.

However Plasma tvs charge a gas to a plasma 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. 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 or on movies the amount of power consumed for plasma tvs will 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. Future plasma tvs are going to consume less than half the amount power consumed at present.

Life expectancy

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 tvs are unfounded.

Conclusion - which should you buy?

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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