How To Understand Plasma and LCD TVs

The two most popular high-tech (and expensive) television sets nowadays are plasma and LCD TVs. They both sport high and crisp resolutions, bright displays, flat and wide screens and thin and compact housings. You can hardly tell them apart simply based on their features. Their fundamental difference however lies in the underlying technology.

Plasma televisions are called so because they make use of plasma display panels (PDP) for their screens. A PDP is composed of two glass panels in between which are numerous tiny cells filled with the inert gases xenon, neon and helium. Also within these glass panels are electrodes lining the back and front of each cell. The control circuitry of the television charges these electrodes in such a way that there is a voltage difference between those in front of the cells and those at the back. This voltage difference also electrically charges the inert gases and turn it into plasma (hence the name). This plasma is filled with ionized atoms of the gases, some are moving and drawn to the front electrodes and the others are moving and drawn to the opposite direction. When these ions collide, light particles called photons are produced. Phosphors which are a kind of substance that retain light when struck by energy coat the back of each cell. When the photons hit this phosphor coating, colored light is produced. Each picture element or pixel on the plasma television screen is composed of a red, green and blue phosphor which can combine to produce various shades of color. The control circuitry varies the electric current running through the cells at a rate thousands of times per second creating a multitude of possible combinations. It is through this that an image is created on screen.

The screen of an LCD TV contains three important components: cold cathode fluorescent lamps, liquid crystal shutters and colored filters. The lamps serve as the source of white light and there are a series of them located at the back of the screen. The white light emitted passes through a grid made up of millions of liquid crystal shutters each paired with a colored filter. These liquid crystals change alignment, opacity and transparency according to the voltage of electricity running through them by the television's control circuitry. Thus the amount of light that passes through is controlled. After the shutters, the light hits the colored filters which could be red, green or blue. They remove all other colors except that which is specific to them. A shutter and its paired filter comprise a sub-pixel. A combination of a red, green and blue shutter-filter pair makes up a whole pixel. By the combined action of every shutter-filter pair in each pixel, various shades of color can be produced and an image is eventually created on screen. These pixels are so small that even from a short distance they will appear as nothing more than a blend of colors.

The pros and cons of each type of television may be due to the technology being used or perhaps the kind of designs employed by their manufacturers. Weighing them, one may not really see a clear advantage for either type. Plasma TVs use up more power and generate more heat but LCDs poorly display dark colors and sometimes can't handle fast moving images. It's really a toss up and only the individual's preference or budget can ultimately be the deciding factor.


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