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Why are Plasma TVs Thin?
Since the birth of television, the vast majority of them have used the same technology; the CRT, or cathode ray tube. CRT’s produce a sharp, detailed image, but they have a serious drawback: they are bulky.

In order to to increase the screen size, the length of the CRT must also be increased, therefore making sets above about a 40" size impractical. (Most projection tvs use CRT’s also, but newer technologies like DLP and LCD have also made them thinner in some newer models.)

Recently, a new alternative has emerged, the flat panel plasma display, or just plasma. These can range in screen size (widescreen 16 x 9) from 37" to 63" and beyond in the next year or two. They only have a depth of about 4-6" even when mounted on a wall.

The basic idea of a plasma display is to illuminate tiny fluorescent lights to make a picture. Each individual pixel consists of 3 of these lights, a red, a green and a blue. Each is very shallow in depth, and filled with a gas (plasma), which is normally in an uncharged state.

When these gas particles are charged positively or negatively, the plasma gas releases photons of energy. Each of the three colors is produced by the interaction of these ultraviolet photons with a phosphor material coated on the inside of each pixel.

By varying the pulses of current flowing thought the different cells, or pixels, the control system can increase or decrease the intensity of each color, and combine them in a way to produce colors across the entire spectrum.

A CRT works in a similar way, in that an electron beam shot from the back (yoke) of the picture tube hits the front inside of the tube, exciting phosphors to produce different colors. But, the picture tube depth is still many, many times deeper than the plasma pixels, which are sandwiched between thin sheets of glass.

The additional depth on the plasma is merely the electronics, fans, connections and cabinet.

Currently, most plasmas are monitors, meaning they don’t have tuners or speakers. Most people use a cable box or VCR for cable TV, and, of course, with satellite dishes you also have a separate box. Many of these sets are also in home theatre systems, where external speakers and surround amps are used for the best sound.

As the popularity of plasmas has increased, and the price has come down, more people are using them for "normal" TV applications. Therefore, many of the models soon coming out will have built in tuners and speakers.

Some prototype sets have even been shown with a floor standing cabinet similar to a console type TV of years gone by.

Greg Thill
M.E.S. Home Theatre

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