Televisions

As with all flat-panel displays, a plasma unit is made up of an array of luminous dots, otherwise known as pixels. Plasma belongs to the genre of self emitting displays, like CRTs (tube televisions) or from organic LED screens which illuminate only where light is actually required. Liquid crystal or projection systems (LCD, DLP, LCoS), by contrast, are so-called light valves working in a transmissive manner, which switch the individual pixels to transparent or dark and necessitate a backlight.

The light is produced by different phosphor compositions for each primary color, as with a traditional tube TV. However, they are not excited by an electron beam, but rather by infrared light that originates from gas discharges - similar to the glow of a neon tube. Applied energy rapidly turns the gas into a plasma state - the fourth physical state a material can possess along with solid, liquid and gas. In this state, the material emits photons - or light. To convert this light into the familiar full-color display, a rather long-winded approach is taken that uses infrared and different phosphors.

The gas is held in cells which define the pixel dimensions and is separated by minute filaments between glass plates. The base and sides are coated with phosphor, and allow light to be emitted through the front. Electrodes on both the front and rear of the glass deliver the necessary voltage for the gas to discharge and illuminate the pixel. The very nature of the physics behind the principle means that the plasma is not in a permanent 'on' state thereby continually illuminating the pixel, but bursts into activity when excited.

For continuous illumination this discharging needs to be repeated in exactly the same manner as a neon tube is with a 50 Hz or 60 Hz AC cycle. But, because the complete gray scale spectrum needs to be represented, it is not just a case of switching the pixel on or off. Instead, it is essential that the gas is rapidly flashed, and the more rapid the burst interval, the greater the illumination - and this is exactly the manner in which the brightness is controlled. The visual conception of the various brightness levels attainable on plasma displays is nothing more than an optical illusion. Placing three cells coated with red green and blue phosphors next to each other creates a single pixel capable of producing colored light.

Special Case - Plasma Screen from Tubules:

Normally, a plasma panel has channels comprised of coated glass plates. Shinoda-Plasma, a Japanese corporation, has developed another principle that creates a screen from thin tubules. Each is around a millimeter thick, and three of them placed next to each other deliver the necessary color that makes up a TV picture. The individual tubules are kept together with a foil, which also contains the excitation controller.

This method permits the manufacture of near unlimited screen sizes which can also be marginally cambered or curved transversely to the tubules. The manufacturing costs are reasonably low and the set itself is relatively light. The larger pixel dimensions of the Shinoda screens make them unsuitable for living-room viewing, but are an excellent choice for scoreboards or advertising display panels for public viewing.

The company founder, Tsutae Shinoda is recognized as being one of the fathers of plasma technology in Japan, and led the engineering team for screen development at Fujitsu, who brought out its first plasma screen, a 42" unit in 1997. When Fujitsu handed over its plasma unit to Hitachi, he became self-employed.

Plasma Screen from Tubules