Abstract: Two sheets of material at least one of which is transparent, the sheets being overlaid one upon the other and sealed together to form a gas-tight enclosure. One or more gas discharges can be initiated within the enclosure between a pair of electrodes along a predetermined path, the gas discharge path or paths comprising a plurality of adjacent elongate portions extending between and generally parallel to the sheets. The electrodes may be exposed within the enclosure and connected to a DC or AC electrical power source. Alternatively however the electrodes may be electrically insulated from the enclosure but connected to a high frequency AC electrical power source. The enclosure may be filled with low pressure gas in the manner of conventional discharge tubes.