Calibration procedures of a ccd camera for photometric measurements

Abstract

Present technology allows to produce high resolution and low cost CCD (Charge Coupled Device) cameras. Videography uses this kind of camera to make up innovative measurement instruments, above all with reference to luminance and lighting level a surface. The main advantage of CCD photometer is the possibility to collect, in a much shorter time and at a higher resolution with respect to the traditional luminancemeters, large quantity of measurement data referred to extended surfaces. This in turn leads to a simpler and faster measurement procedure when the evaluation of luminance distribution an extended surface is required rather than the knowledge of luminance values in few single points. The knowledge of videographic technique and of the related calibration problems is essential to set up a CCD photometer. Photometric measurements based videography require calibration procedures concerning several aspects, depending CCD sensor, optical system and coupling camera-optical interface. This paper refers to the main problems in the set up of a CCD photometer: zenith (or on axis) calibration, vignetting characteristic of the instrument, background influence in the photometric measurements and spectral response. The interesting obtained results have allowed to complete the set up of this innovative luminancemeter for lighting research and application, particularly for indoor built environment.