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LCD or Plasma television - which one is the best ?

View PDF | Print View | Html View Written by: Armadeus Cornelius
Total views: 7 | Word Count: 2132 | Date: Sat, 21 Nov 2009 | 0 comments

Comparison of the flat screen tv 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 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

The screen of a Plasma tv is made up of millions of microscopic gas filled glass cells which have electrodes in them. The cells are filled with inert gases including xenon and neon and form each pixel. When a current is applied to the cell electrodes the gas atoms become 'excited' and become a plasma emitting photons of ultraviolet light. When the photons strike the phosphor coating that is inside the glass cells light is emitted. The light colour emitted is determined by which of the three coloured phosphors are used - Red, green or Blue. These colours can be combined to produce billions of colours. When millions of the pixels are combined they form an image on the screen like LCD televisions. Plasma tvs are only manufactured by Panasonic, Philips, Pioneer, LG, and Samsung and are available in range of sizes from 32 inches through to 150 inches.

A comparison of the Picture quality and Performance

Screen Brightness

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.

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 the main a high ratio means greater details can be discerned. Historically LCD tv panels have had a lower contrast ratio than plasma tvs because the backlight bleeds through darkened pixels and lightens the image. Recent advances in technology have created techniques to avoid light leakage, and improvecontrast 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.

Colour Saturation Levels

The colour saturation measures the accuracy of how colours are presented on the screen in the presence of grey shades. A higher grey shade will result in lower colour saturation. The colour saturation of a Plasma tv screen is high because of their black levels, their low grey shades, and their ability to switch off pixels when they aren't in use, thus preventing colours being diffused by the stray light emissions. Hence the tints and hues are visibly more colourful and more life like.

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

The screen resolution is a measure of the total pixels that makes the screen. The higher the definition, the higher the resolution and greater the detail and sharpness will be in the picture. LCD HDTVs have a resolution'20 pixels x 1080 pixels or 1080P are, size for size, at a lower price than comparable Plasma tvs. 1080 is the vertical reolution and the P is for progressive scan because it isn't interlaced. The best Plasma tv and LCD tvs screens above 37 inches are HDTVs with the same 1080P resolution i.e. there is no difference. At sizes of 37 inches down to 32 inches the best LCD tv screens are still 1080P set but the Plasma tvs are lower resolution HD ready 720P (1280 pixels x720 pixels) models. There aren't any Plasma tvs smaller than 32 inches, but there are many LCD tv models.

Refresh Rate and Response Time

These two attributes in combination influence how fast a moving picture a screen can reproduces without the image blurring. Response time is a measure of how quickly 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.

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.

The Viewing Angle

This is a measure of how far off axis you can view the picture before it fades. The viewing angle of a Plasma television is between 160 degrees to'0 degrees. On an LCD television the viewing angle is about 100 degrees at which point the picture dulls.

The screen surface of lcd tvs and plasma tvs

Plasma tvs have reflective shinny screen surface which can be affected by glare depending on the viewing conditions. Lcd tvs have a matt finish which reduces glare.

Image 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

image retention is often confused with burn-in which has similar characteristics. However image retention is a 'ghost image' that appears on a plasma tvs after a still picture has been displayed for an extended period of time, but then disappears when a bright new image is displayed. Or it vanishes after a few seconds. By having a 'break in' period of about 100 hours from new, this can be minimised. Whist watching programs during this break in period care should be taken to watch programs that don't have any static bright images like station logos and scrolling news headlines at the bottom of the screen. Also try to watch programs that fill the whole of the screen. It recommended that during this period the brightness and the contrast is kept at about a mid level. These characteristics of image retention and burn-in have been greatly reduced by technical improvements to reduce the possibility of 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 constantlyon and uses virtually constant power. LCD tvs usually have an adjustable back light which uses more 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.

Though Plasma tvs charge a gas to a plasma to generate light. The more light that is necessary 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. Accordingly the power consumption varies.

On paper it might seem that the Plasma tvs employ a lot more power than LCD tvs. Plasma tv manufacturers have a tendency to quote the most power usage at full brightness. However 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 watching mainly dark programs and movies the average power power consumption of an equal sized plasma tv is really lower than LCD tv. On the other hand if lots of cartoons and sport are viewed then the LCD tv uses less power. Consequently 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

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

Conclusion - which is the best?

Plasma televisions and LCD televisions both have advantages and disadvantages. LCD tvs have higher brightness, no concerns about screen burn, and they are thinner and lighter. But Plasma tvs have a better real world picture with a higher contrast, blacker blacks, and more natural colours than LCD tvs. Obviously not all Plasma tvs are better than all LCD tvs. A top specification LCD tv will out perform a cheap plasma tv. If you weigh up the advantages and disadvantages a good plasma tv is the best option but you do get what you pay for.

About the Author

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