The spectral pulse shape of Cherenkov lights was directly measured by using cosmic muons. The observed decay times for early and late timing were 5.0 and 5.2ns, respectively. They were actually shorter than the time of scintillation lights which were also measured as 9.3ns and 9.2ns, respectively. However we could not see the difference of the rise time between scintillation and Cherenkov lights. This was due to the slow response of our DAQ equipment, photomultiplier and FADC digitize
