An electrochromic large area device has been produced by Isoclima using a physical vapour deposition technique. The electrochromic coating has a five layer thin him structure and all the layers have been deposited in the same vacuum environment using the same technique. Two specimens with different sizes, 50 x 50 mm(2) and 300 x 300 mm(2), were prepared to be submitted to spectrophotometric and variable angle photometric characterization, respectively. The surface density of charge in both states (coloured and bleached) was obtained from the voltage step response recorded in terms of current density versus time. These measurements were performed during the spectrophotometric and photometric characterizations. Colour and (near) normal incidence luminous and solar parameters of the electrochromic device were obtained by suitable integration of spectral transmittance and reflectance curves. Luminous transmittance and reflectance values of the electrochromic device under collimated variable angle or diffuse irradiation were directly measured by photometry. The photometric data were used to simulate the performances of the electrochromic device used in real conditions as a transparent part of a large window of a room. A computer code named Heatlux was used to evaluate the luminance distribution on the working plane in the room. Location of the building, orientation of the facade, geometry of the room, wall thickness and size of the windows were all considered in the simulation.