This plot just shows the aggregate radiance in ultraviolet and visible wavelengths -- all wavelengths -- seen by one of LCROSS' spectrometers after the Centaur hit the Moon. Not much can be read from this graph except for the very, very good news that they did detect the flash, which means that buried in their spectral data should be good information on what was in the subsurface where the Centaur hit.
NASA / GSFC / annotations by Emily Lakdawalla
Spectrometer data from LCROSS after impact
The LCROSS visible spectrometer swept across the sunlit rim of Cabeus crater before the impact, then into darkness, whereupon the reflectance drops very sharply to a flat low. Then it swept across the impact site, where it detected a tiny "blip" from the impact. The sharp peak following that results from a known instrument artifact that had yet to be calibrated out in this early version of the data.