Setting up a CCD photometer for lighting research and design

Recent availability of video-cameras with CCD-type sensors (charge coupled device) has proved to be particularly stimulating for all those applications requiring photometric measurements, above all for the measurement of luminance values related to the physical and technical qualities of a built environment. This method allows the instantaneous capture of an image, thus enabling collection of luminance values relating to the points of measurement; this in turn leads to the evaluation of luminance distribution and lighting levels of the surfaces that make up the environment. Setting up this system requires the following basic configuration: a photopic filter V(λ), an optic interface, a computer equipped with an appropriate card for the capture and digitalisation of the acquired image (the “frame grabber”) and, finally, suitable software for the processing of collected data. In this article a detailed description of this acquisition system is reported, and subsequently a report on the procedure adopted for its calibration so as to enable the capture of relevant photometric values. Final analysis and validation of results are carried out by means of field test. A case study of CCD photometer application has been then performed using a basic software tool autonomously developed to evaluate indoor lighting level; the luminance map of a diffuse light source has been used as “input” data for the developed software, and the “output” data, i.e. illumination levels, have been then compared with measured values.