Rapid determination of the photometric bidirectional scatter distribution function by use of a near-field goniophotometer

The bidirectional scatter distribution function (BSDF) characterizes the scattering properties of a material for any angle of illumination or viewing, and offers as such a complete description of the spatial optical characteristics of the surface. An accurate determination of the BSDF is important in many scientific domains, such as computer graphics, architectural and lighting design, and the field of material appearance characterization (e.g. the color and gloss properties). Many BSDF measuring instruments have been reported in the literature. The majority of these instruments are goniometric measurement devices, by use of which the BSDF is determined by scanning all incoming and outgoing light flux directions in sequence. For this, the sample, detector, and/or source perform relative individual movements. In result, the major restriction of this type of instruments constitutes the measurement time, which may run to the order of several hours depending on the accuracy (angular resolution) and the complexity (spectral coverage, absolute measurement capability, etc.) of the reported measurement data. This paper describes the results of a feasibility study, in which an alternative goniometric measurement system is designed, enabling to acquire the photometric BSDF in a full three-dimensional (3D) space, with a high mechanical angular resolution (0.1°) in a time efficient way (about 30 minutes). A near-field goniophotometer, originally intended to measure luminance intensity distributions and luminous fluxes of light sources and luminaires, was converted for this purpose. Besides a discussion of the design and the measurement procedure, test sample measurements are presented to illustrate the versatility of the device.status: publishe