Comparison of the flat screen tv technologies

When it comes to flat screen TVs the two technologies LCD and Plasma seem 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 stores, there are various differences between the two technologies.

LCD screens explained

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 tv screen comprises of millions of minute ‘light bulbs’ which are tiny 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 LG, Samsung, Panasonic, Pioneer, and Philips. Plasma tvs are existing in sizes from 32 inches to 150 inches.

Performance and Picture quality compared

The Brightness of the picture

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.

Contrast Ratio and Black Levels

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

This is a gauge of the correctness 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 capability of Plasma tv pixels to be turned 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 number of colours that can be displayed. The most expensive models are now claiming to have colour gamut’s getting rather 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 except 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.

Resolution

This is the amount of pixels that make up the screen. The higher the resolution is, the higher the definition and the sharper picture is. Currently, LCD HDTV’s produce the image at’20 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 of the screen

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 fast 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 generally caused by the refresh rate, or the 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.

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’0 degrees whereas LCD tvs have a viewing angle of around 100 degrees after which the picture dulls.

The surface of the screen

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.

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

Numerous people mix up burn-in with image retention which is very similar. With image retention the ‘ghost image’ disappears quickly either as soon as a new, bright image is displayed or after a few seconds. image retention is infrequently noticed but normal on plasma tvs because of the technology utilized, but it can be minimised by having a ‘break-in’ period when the plasma tv is first bought. The break-in period usually lasts 100 hours, during this time you should not view any programs that do not fill in the whole screen, and you should notview any programmingthat have static images such as bright station logos or news scrolls at the base of screens, and you ought to lower the contrast and brightness to a middle point. Nowadays there are also features built in to the plasma tvs to lower the likelihood of either burn-in or image retention.

[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.

Though Plasma tvs charge a gas to a plasma to produce light. The more light that is necessary the more often this is done. So it’s usual for plasma tvs to need more energy on an image with high levels of brightness, and less energy on low brightness scenes. Consequently 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 at this momentquoting statistics of 100000 hours for the life expectancy. This represents a running level of just about 11.5 years of non stop use. As a result any concerns about the life expectancy of plasma tvs being less than LCD tvs are unfounded.

Conclusion

Both technologies have advantages. Plasmas tvs typically have a superior subjective picture with healthier black level, higher contrast, and better colour rendering than LCD TVs. While LCD TVs have higher brightness, and no screen burn-in worries, and are lighter and thinner. This is not always the case sincea good LCD TV might have a better picture than an middling or poor plasma TV. But on balance I consider that a plasma tv is the better option with more advantages. Ultimately you get what you pay for so spend as much as you can find the money for on you preferred format.

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