This paper presents a gray box model of a photovoltaic (PV) cell working under low illuminance artificial indoor lighting conditions. A mathematical model of PV cells with single and two diode configuration is used. Additionally a platform for the measurement of the PV cells within the indoor environment is presented. An optimization problem is formulated to tune the internal parameters of the mathematical models according to the collected data from measurement platform. Fluorescent and halogen lights are used as two common indoor lighting sources.The fine-tuned mathematical model with calculated parameters is implied to evaluate the performance of the gray box model compared to the measured data.Finally, to avoid using multiple models for different environmental conditions, regression techniques are used to generalize the model only based on the irradiance.