The generation of intense cavitation luminescence flashes by the use of an improved U-tube apparatus is presented. The light flash was characterized by its high energy ( approximately 1.4 mJ) and long duration ( approximately 200 mus) that allowed the time-resolved spectrum to be measured for a single flash. The C2 molecular vibrational band emission superimposed on a continuum background spectrum was observed and found to be delayed in time with respect to the background emission. The dependence of pulse width on the luminescence wavelength and the coincidence of the surface brightness with the blackbody radiation behavior suggest the blackbody mechanism of the luminescence.