Polarity of a solvent can be defined by the Onsager function or the Debye function, which both are functions of the static dielectric constant. Polarity has also been shown to be related to the solvatochromic shifts of the absorption and fluorescence spectra. In this study, the emission maxima of the probe molecule Nile Red were taken in different solvents of known dielectric constants, and relationships between the emission maxima and the Onsager and Debye functions were established. These relationships were used to estimate dielectric constants for various environmentally benign esters.