Waveforms of return-stroke-like current with fast fronts are produced by an impulse current generator in the 15 mm open-air discharge gap in the high-voltage laboratory. The waveform characteristics of channel luminosity for currents with positive and negative polarities are compared. The influence of the observation azimuths is also investigated.Results show that

for the negative current

there exists a "hump" along the falling edge of the luminosity waveform

whereas this phenomenon does not exist for the positive current; when the arc discharge is observed from different directions at the same distance from the discharge gap

the observation azimuths seem to hardly affect the resultant channel luminosity. Moreover

by adjusting circuit parameters

26 sequences of the channel currents which contain a total of 200 pulses

with a current amplitude ranging from 2.96 to 29.04 kA

a current 10%～90% risetime ranging from 2.11 to 9.52 μs

and a current half-peak width ranging from 15.92 to 172.83 μs

are measured. The current waveform has a relatively short risetime and a relatively slow decay

similar to the luminosity waveform which consists of a rising edge faster than the current and a falling edge that is initially fast and become slow at last. Analyses of parameter correlations are conducted between the channel current and the corresponding luminosity. Linear correlations have been found not only between the current peak and the luminosity peak

but also between the current 10%～90% risetime and the luminosity 10%～90%risetime. However

no direct correlations are observed between their half-peak widths. The correlations between laboratory generated return-stroke-like lightning current and the corresponding luminosity are similar to those found in the return-stroke current in naturally-occurred lightning.