Optical and electrical properties of undoped ZnO films were investigated in this study. We find that the conductivity increased with increasing the ratio of (blue luminescence+green luminescence) to ultraviolet luminescence [i.e., (BL+GL)/UVL] defect emission intensities, due to the increase of the singly ionized oxygen vacancy. We deduce that the BL and GL are related to the oxygen-vacancy deep level and the yellow luminescence is attributed to the band-acceptor transition. We also find that poorer crystal quality may lead to the reduction of the optical transmittance. This suggests that these defects and the crystal quality interact to change the conductivity and optical transmittance of ZnO. The spectroscopic correlations may be used as a predictive tool to identify the quality of ZnO.