Large, flat television screens, up to 127 cm in the diagonal, that can be hung on the wall may soon be available. Japan-based Sony and an American electronics company, Tektronix, have jointly built a flat TV based on liquid crystal display (LCD) technology that can produce high resolution, high-contrast images comparable to those produced in the convention.11 TV sets.

With the existing LCD technology, it is difficult to make large, Flawless screens. Colour screens are composed of thousands of liquid crystals which either block light or allow it to pass through, depending on whether they have voltage across them.

The voltage in each crystal is governed by an electronic switch - some of the switches tend to develop faults during manufacture which show up as bright dots on the screen. With large screens, the chances of finding faults is so large that they cease to be cost effective.

The new TV - tentatively called Plasmatron - overcomes this problem by dispensing with electronic switches and instead has for each horizontal row of crystals a long plasma discharge channel filled with low pressure gas. When a high voltage passes between the electrodes running along the channel, electron clouds are formed.

The plasma channel acts as a common electrode for all liquid crystals in that row. With only one channel for each row, the chances of proclucing a flawless large screen become much greater than with conventional LCD technology. Some hopes that the new sets will be A ready for sale by the middle of 1996.