Light curves of the 12 μm emission following the collision of Shoemaker-Levy 9 fragments A, E, H, L, Q1 with Jupiter are presented. Impacts F, P2, Q2, T, U were monitored, but not detected. The observations were carried out with the Saclay CAMIRAS camera mounted on the 2.56 m Nordic Optical Telescope located at La Palma (Canary Island, Spain). Of particular interest is the light curve of the L impact (the brightest impact), where 3 different regions can be observed. A precursor flash (the debris cloud rising above the limb) is detected about 1 min 30 s after the detection from the Galileo spacecraft. Twelve minutes later, a huge infrared spot at a temperature of about 700 K appears at its peak intensity: 13000 Jy. A new change of behavior is observed 20 min after impact: a secondary bump appears, after which the flux decreases at a slower rate. Light curves of impacts Q1, H, E and A, up to more than one order of magnitude fainter than the L impact, are quite similar. Ballistic re-entry of dust-gas in the atmosphere must be considered in the interpretation of the IR spot.