For two decades, DSSC's have shown promising performance for high yielding conversion of solar energy to electricity under mild conditions. However, the related investigation techniques rely either on pure electrochemical techniques regardless of the light source wavelength either on photochemical processes with a poor electrochemical description. The present study aims at bridging together these two domains using electrochemical impedance spectroscopy (EIS) through wavelength scanning using a monochromator. The main electrochemical features of the DSSC and parameters of the EIS model were examined depending on light wavelength. The technique has been developed at open circuit voltage, using the Ru-based N719 sensitizer impregnating a thin mesoscopic TiO2 layer, with I-2/I mediating redox couple. Tests were carried out with and without mediator, thus resulting in precise interpretation of the various electron transfers occurring at the photo-anode. The time constants of the various processes involved could be obtained without the use of transient absorption or emission spectroscopy: comparison of the data with formerly published results could validate the original method. Moreover interpretation of the wavelength-dependent spectra revealed the existence of two deactivation processes in the cell - which have been identified and quantified - depending on the density of excited states generated at the SC-electrolyte interface. Finally, in relation to IPCE measurements and absorption spectra, the exchange current density of the cathode for I regeneration was also found affected by wavelength. The approach could be applied to non-zero currents and to other sensitizer-semiconductor systems.