High-Definition LCD Screens

LCD, short for (Liquid Crystal Display) is most popular the alternative to plasma displays in the consumer space.

LCD Display Technology

Most basically LCDs produce the image you see by blocking or emitting the light from a backlight using liquid crystals sandwiched in between two glass plates. This is the same principle used in the liquid crystal displays found in everyday items such as digital watches, but improved and updated in a much more advanced implementation.

LCD PixelAn Exploded View of a Single LCD Pixel

An LCD display is made up of a thin layer of liquid crystals arranged in a matrix (or grid) of a million or more pixels (picture elements), which are themselves made up of three sub-pixels aligned to a colour filter for each of the primary colours; red, green and blue. This layer is sandwiched between the two glass plates, which are covered in a matrix of electrodes and transistors (electronic switches), each coated with a polarising filter. The two polarising layers only allow light vibrating in one direction to pass through them, one allows horizontally vibrating light through and the other passes vertically vibrating light.

The light source in an LCD is its backlight so this unpolarized light becomes vertically polarized as it passes through the first polarizing filter at the back of the display. The other polarizing layer on the front sheet of glass is horizontally polarized, so ordinarily the now vertically polarized light coming from backlight can't pass through it. The role of the liquid crystal layer in the middle of the display is to rotate the vertically polarized light travelling through it by ninety degrees so it can pass through the front, horizontally polarized filter. By varying the voltage applied to the liquid crystal sub-pixels the amount they twist the light changes, allowing more light of each colour though as a greater voltage is applied.

Individual pixel colours are produced by the combination of the primary colours produced by each sub pixel, with the pixel's overall brightness is produced by the sub-pixels relative intensities. Many thousands of these pixel units operating together in the display combine to produce the image you see.

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LCD vs. Plasma Note

The real 'truth' about LCDs vs. Plasma is that neither technology is inherently or necessary better than the other. LCD and plasma technologies are constantly converging to the point of being equal in terms of an everyday viewing experience. The advice below represents a general, current overview of the pros and cons of each display type, but there simply is no substitute to taking the time to experience both technologies for yourself before making a purchasing decision.

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Advantages of LCD Displays

Good LCDs are able to produce high and more consistent contrast ratios than some plasma displays, and may appear brighter if they have a powerful backlight or are viewed in high ambient light conditions where plasmas tend to perform worse.

Typically LCD display technology will use less power and generate less heat than an equivalent plasma display. LCDs generally consume the same amount of power as older CRT screens, where plasmas will tend to consume more, although this comparison really depends on the size of the displays being compared.

LCDs are also available in a wider variety of sizes than plasmas, ranging from 15 inches upwards, where plasmas start at around 37 inches. This can make them more flexible, and suitable for more locations within the home.

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Disadvantages of LCD Displays

Some LCDs may advertise lower contrast ratios than plasma displays, however whatever the quoted figure, LCDs commonly struggle to produce blacks and dark colours as well as those produced by a good plasma display. Leakage of the backlight through panel always occurs to some extent and is most visible when displaying black and dark images. Manufactures are stating to address this problem however, with dimmable backlights which dynamically adjust to the brightness of the image being displayed.

Liquid crystal displays have always had a reputation for difficulties displaying rapid motion, often know as ghosting or blurring, caused by the slow response (change) time of the liquid crystals. This may still be a issue for lower-end displays but more rapidly changing liquid crystal technology is readily available with this now only really being to be a problem for lower quality and older displays.

Because an LCD's backlight is always on, these displays can suffer from the effects of retinal persistence or 'hold' where the eye briefly retains an impression of last thing it saw (for an extreme example look at a light bulb for a few seconds then look away or close your eyes). The problem with retinal persistence mainly affects motion portrayal and is beginning to be addressed by manufacturers using techniques such switching off the backlight briefly during each frame.

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