In this paper, we introduced the super-bright blue-purple light emitting diode (LED) into a novelty light resource which excited chlorophyll-a to emit fluorescence. Furthermore, we compared LED with the ordinary excitation resource. By two experiment apparatus, we have measured the fluorescence signal and obtained the chlorophyll-a fluorescence emission spectra. The results show that LED can act as an alternative excitation resource in developing the fluorometer for the in situ measurement of the chlorophyll-a concentration in water.