The lack of knowledge concerning the commissioning of a daylight responsive system constitutes a serious impediment to their widespread use. Furthermore, installation details and tools regarding their photosensor position and field of view (FOV) are insufficient. This paper presents a decision making method capable to estimate the best position of a photosensor on the ceiling and its proper FOV based on multiple criteria analysis. The criteria used are (a) the correlation of the lighting levels between the working plane and the ceiling, (b) the corresponding energy savings and (c) the lighting adequacy which is defined as the percentage for occupied time with total illuminance exceeding design illuminance (i.e 500 lux EN 12464-1, 2011) and is strongly affected by the control algorithm.

A number of simulations with variable FOV and position of photosensors were performed in order to clarify the calculation procedure of the proposed methodology. Three different typical room geometries have been used with variable window sizes and orientation. Furthermore a prototype photosensor with variable FOV through the use of a telescopic cylinder was constructed and placed in a scale room (1:10) in order to verify the results of simulations. The verification was based on a set of experimental procedures concerning measurements of the spatial response of the prototype photosensor (for various FOVs) and measurements of ceiling/workplane illuminance inside the scaled room for various combinations of position and FOV of the photosensor. The proposed methodology can be used as a tool for the determination of the optimum operation of a daylight responsive system with photosensors.