The input circuit of the lightning-flash counter adopted by Study Committee 8 of the Conference Internationale des Grands Reseaux Electriques is intended to have a threshold of 5 v/m and, consequently, also has a calculable response to ramp changes in the electric field. It is shown that, for ramps of sufficient duration, either a positive ramp or a truncated negative ramp of slope 6000 (v/m) sec−1 will cause the counter to register. Electric field changes caused by identified lightning flashes have been analyzed in terms of steps and ramps, and magnitude distributions of these have been obtained. The distributions were used in conjunction with the threshold of the counter to steps and ramps, and the fraction of flashes that cause the counter to register was calculated for various distances between counter and flash, using the inverse cube law of variation of field change with distance. The effective ranges for ground and cloud flashes were calculated to be 30 and 20 km, respectively. The method described is applicable to any simple flash counter using detection of electric field changes.