an electric discharge tube in which an electric luminous discharge is to be produced for display purposes has internal electrodes connected to a generator providing an alternating voltage of cyclically varying magnitude . at least one external electrode extending lengthwise of the tube is connected to one generator terminal by way of a reactance , preferably a capacitor . the external electrodes may be wire or thin metal strip and are preferably adhesively secured to the tube envelope . a plurality of such tubes may be connected in series to a single voltage generator .