Are there any differences between the two technologies?
When it comes to flat screen TVs the two technologies LCD and Plasma seem very alike with almost lifelike images and the ability to be hung on the wall. Although LCD tvs and Plasma tvs displays may look very similar in the shops, there are various differences between the two technologies.
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 plasma tvs works
A Plasma tv screen comprises of millions of tiny ‘light bulbs’ which are tiny glass cells filled with inert gases such as xenon and neon. These cells are illuminated 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 strike a phosphor coating which emits visible light. The colour of the visible light emitted by each cell depends on the three different coloured phosphors – green, blue and red, and can together make billions of colours when combined. As with the LCD tv screen, the millions of cells combine to form the image on the screen. Currently the only manufacturers of Plasma tvs in the UK are Panasonic, Pioneer, Philips, LG, and Samsung. Plasma tvs are available in sizes from 32 inches to 150 inches.
A comparison of the Picture quality and Performance
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.
Black Levels and the Contrast Ratio
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
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.
TV Screen 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 1920 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.
Response Time and Refresh Rate
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.
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 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 screen surface
LCD tv screens are available with matt finish screens which reduce glare whereas Plasma tvs have a reflective screen.
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.
Power consumption
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.
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 might appear 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. But the plasma tvs power power consumption varies depending on the signal and the amount dark and bright areas on the screen. Studies have shown that when watching predominantly dark programs and movies the average power power consumption of an identical sized plasma tv is really lower than LCD tv. However if lots of cartoons and sport are watched then the LCD tv consumes less power. Accordingly 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.
Plasma tv Life expectancy
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.
Conclusion – which should you buy?
Both technologies have advantages. Plasmas tvs generally have a superior subjective picture with healthier black level, higher contrast, and better colour rendering than LCD TVs. Although LCD TVs have higher brightness, and no screen burn-in worries, and are lighter and thinner. This is not always the case becausea good LCD TV could have a better picture than an average or poor plasma TV. Although on balance I think that a plasma tv is the better option with added advantages. Ultimately you get what you pay for so spend as much as you can manage to pay for on you preferred format.
