The light curve of the impact sites on Jupiter of the fragments of Shoemaker-Levy 9 exhibits some characteristic features, which have been retrieved for several impacts, and must therefore correspond to different steps in the release and dissipation of the kinetic energy deposited during the impacts. Accurate geometric calculations are presented, which allow us to estimate the possible altitude of observable events in the light curve. A radiative transfer calculation made at 3.5 &mgr;m shows that a hot spot in the atmosphere can indeed be observed at emission angles as large as 95¿, at pressure levels of 10-100 &mgr;bars. Observations taken simultaneously on impact H and L between Pic-du-Midi observatory (imaging at 1-2 &mgr;m), ESO/NTT (3.5 &mgr;m imaging spectroscopy for H only) and NOT (imaging at 10 &mgr;m), are analyzed to search for wavelength variations in the light curve. It is found that the time of occurrence of the precursor observed just before the main event in the L light curve is shifted by ≈1 minute between 1.2 and 10 &mgr;m observations. The observations of the later stage (on impact H) show a similar shoulder in the decreasing part of the light curve. A spatial extension of the emissions could possibly explain the observations. ¿ American Geophysical Union 1995