Characterization and calibration of a CCD detector for light engineering

This paper describes the methodology followed for characterizing a commercial CCD camera as a luminance meter for measurements in road light plant. Actually several commercial CCD cameras have been proposed on the market for this type of application and they are sold with full working software including a factory calibration in luminance units (cd/m²). In fact the availability of a high number of closely spaced small detectors (pixels) on a single chip permits analyses almost impossible or very time consuming if carried out with traditional instrument. These devices are sold at prices lower than scientific grade CCD cameras that usually are not commercialized with a V(λ) filter and therefore they could not have a calibration in luminance units. The main counterparts are in the difficulties to define accuracy of measurement, in the low resolution of the A/D converter and in the characteristics of CCD sensor itself. To obtain the best possible results with this type of luminance meters it is necessary to reach a complete metrological characterization and to quantify all the possible effects that could degrade their performances in real measurement situations. In this way the measurement uncertainties might be evaluated correctly and the results could be corrected, if necessary, with ad hoc algorithms.