The precise daylighting simulation in buildings can potentially contribute to designers’ and occupants’ smart utilization of it. The traditional method of employing sky models was indicated with noticeable errors in transient lighting simulation for complex fenestration systems (CFS), due to the mismatch between the real sky and standard sky models. This paper evaluates the performance of a calibrated embedded photometric device based on sky luminance monitoring, capable of real-time on-board lighting computing. Daylighting experiments for external Venetian blinds (EVB) were conducted in a lighting test module to demonstrate its accuracy in the simulation of horizontal work-plane illuminance. The BTDF of the EVB was generated for two different tilt angles of slats respectively. With partly cloudy skies, the photometric device was validated with improved accuracy in simulating the work-plane illuminance distribution compared with a common practice employing the Perez all-weather sky model.