Given data represent a spatiotemporal variation of the measured argon emission at 750.39 nm around breakdown during the first half-period. The first column contains the values of the distance in the gap given in units of meters, while the first row represents a time given in units of seconds. The data are obtained for p = 300 mbar, U_0 = 1.5 kV and f = 24 kHz and normalised with respect to their maximum values.