The integration of powerline communication (PLC) with visible light communication (VLC) has attracted the attention of many researchers. Cascading these two techniques offers the possibility of performing a wired transmission over existing powerline infrastructure and a last-mile energy-efficient wireless transmission through pre-installed LEDs for indoor illumination. Therefore, VLC should be deeply analyzed to optimize its integration with other systems. So far, most research has only modeled the channel and modulation bandwidth of the VLC system. However, the electrical and optical aspects are rarely taken into account and there is no explicit expression of the received signal as a function of that emitted. So in this paper, An explicit expression is proposed allowing a direct calculation of the photo-current as a function of the transmitted current taking into account the optical, electrical, and frequency behavior of the VLC system. This expression is validated using measurement results.