lightning impulse a voltage impulse of a specified shape applied during dielectric tests with a virtual front duration of the order of 1 microsecond and a time to half value of the order of 50 microseconds GRM: n. Note: the lightning impulse is defined by the two figures giving these durations in microseconds, especially for standard lightning impulses 1.2/50 microseconds References: SEEswitching impulse SPEchopped lightning impulse SPEfull lightning impulse