Light energy conversion efficiencies of locally isolated strains of Chlorella, Scenedesmus and Chlamydomonas were determined under artificially illuminated and outdoor, directly sunlight irradiated conditions respectively. In the former series of experiments, the values of efficiencies were found to vary from 0 0322 to 0.144 in different experimental sets In the outdoor experiments, the corresponding values were found to be in the range of 0.0175 to 0.0227 in the various sets. The effect of variation of irradiance, temperature and nitrogen source on the energy conversion efficiency was also studied. Urea was found to be the most suitable N-source.