 This limit is the Townsend discharge breakdown voltage, also called ignition voltage of the tube.The occurrence of Townsend discharge, leading to glow discharge breakdown shapes the current–voltage characteristic of a gas-discharge tube such as a neon lamp in a way such that it has a negative differential resistance region of the S-type.The negative resistance can be used to generate electrical oscillations and waveforms, as in the relaxation oscillator whose schematic is shown in the picture on the right.