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Published:April 6th, 2007 16:12 EST
HDTV: What the Letters Mean

HDTV: What the Letters Mean

By George Gildersleeve

HDTV, EDTV, LCD, DLP, LCoS, what do these all mean? Well, in short, these are all types of digital television sets. Analog TVs are no longer being manufactured in the US.  The article will explain the differences in all of these televisions and get you more acquainted with the abbreviations as well as explain the benefits and shortcomings of each type. 

Almost everybody has heard of HDTV is; these letters stand for High Definition Television. This present time and the near future are incorporating HDTV in more areas and various media solutions. High definition is in contrast to Standard definition, the difference being in the number of lines that make up the picture. Standard definition (what has been in use since the televisions inception) makes a picture out of 480 lines which refresh one half at a time. High definition on the other hand, makes a picture out of 720 or 1080 lines which refresh themselves all at once in the 720 line version and some of the newer 1080 sets, or alternately in most 1080 line sets.

The most traditional type of HDTV is rear-projection. Rear Projection sets display a picture that is projected onto your screen by 3 lamps in the back of the set, 1 lamp for each color of red, green, and blue. This type of set does not have a high chance of `burning` an image onto your screen by keeping it turned on with a static image for too long. The downsides to these TVs are the rather large size in comparison to other sets, and the lamps in back can be thrown out of alignment.

The type of HDTV that most movie theaters use is front-projection monitors. These are the types of set that have a projector in front of the visible screen. The picture is displayed on the screen from the projector showing the picture on the screen by means of shining it directly onto the screen. The major disadvantage to these systems is the fact that the picture gets blocked if anything gets in front of the projector. The good thing about these is the fact that in relation to other sets they`re pretty inexpensive in general. Also, newer projectors can be pretty close to the screen and still show the whole picture in its full HD glory.

The next HD display type is DLP which stands for Digital Light Projection. The thing that sets these sets apart from the others is the DLP chip inside the TV that was developed by Texas Instruments to make rear projection TVs thinner. The DLP chip (also known as a `Digital Micromirror Device` is a very small device that can contain more than 2 million mirrors! Each one of these mirrors` size is less than 1/5th of the width of a human hair. Each mirror in the chip represents one pixel on the TV (a pixel is a single dot on the screen that makes up the image). The DLP chips perform about 4 different, complicated tasks in the time of 16 microseconds. Light shines onto these mirrors through a color filter to give the picture its color and to produce the picture onscreen. The benefits of a DLP TV are the price, the picture quality, and that they aren`t susceptible to a static image `burn-in`. DLP TVs are also thinner than most rear projection TVs.
The next types of displays are flat-panel displays, which means that they are very thin and in most cases can even be mounted on a wall. The first of these types is the plasma display. While plasma displays are not technically TVs because they lack a built in tuner to get channels, they can be used as TVs with a separate device that does have a built in tuner (these include VCRs, DVD players, and Cable Boxes among others). Plasma displays are widescreen and are about 6 inches thick. The way plasma displays operate is by creating a picture using pixels. Each pixel in a plasma TV is made of 3 florescent lights-- red, green, and    blue. Florescent lights function by mixing free flowing ions with electrons. The pixels in a plasma display emit light by having a particle collide with an atom which causes an electron to jump up to a higher energy level. When this electron falls to its original energy level, it emits its extra energy in the form of light. The atoms used in plasma displays to display light are xenon and neon atoms. When these atoms are "excited` they release light photons. These atoms create ultraviolet light which is invisible to the eye, but are used to excite other atoms to create visible light. Advantages of plasma displays are the thin size, bright display, and high quality picture. The main disadvantage is the tendency to have an image burned into the display.

The other type of flat-panel display is the Liquid Crystal Display or LCD. These monitors have a very low profile and are extremely thin. Like the plasma displays, LCD are technically not TVs, because they don`t have a built in TV tuner; but paired with other devices, it has TV functionality. The technology behind LCD displays is a very interesting one. The matter that makes up the picture is somewhere in between a solid and a liquid-- which explains the name that seems, at first, contradictory. LCDs are made possible by liquid crystals in the nematic phase, which makes them extremely sensitive to electric current and can change how much light is let through them.

These liquid crystals are arranged in different formations by what is called a `director`, which vary from magnets to surfaces with grooves to get the crystals where they need to be. There are 4 main factors that make LCDs possible. 1. Light can be polarized. 2. Liquid Crystals can change and transmit this polarized light. 3. Liquid Crystals can be changed with electricity. and  4. Some transparent substances can conduct electricity. LCDs use polarized light, liquid crystals, and other factors that would take pages to explain, to create the picture that you see when you view one. The benefits of LCD displays are the thin size, it`s resistance to burning an image as opposed to plasma TVs, and the brightness and colors it can vibrantly display. The only real downside to LCD displays is the limitation in size because of price.