At the Physikalisch-Technische Bundesanstalt a new robot-based gonioreflectometer for measuring radiance factor and bidirectional reflectance-distribution function has been developed. The facility enables measurements of the directed reflection characteristics of materials with arbitrary angles of irradiation and detection relative to the surface normal.

The basis for the description of diffuse reflecting materials is the concept of the radiance factor β, or as a quite similar depiction, the bidirectional reflectance distribution function fr. Both characterizations use the concept of the perfectly reflecting diffuser (PRD), which reflects, by definition, the incoming radiation loss-free, completely diffuse and with Lambertian direction characteristics. The PRD is a theoretical concept only, which cannot be realized materially. Since there is no material with these characteristics, the realization is carried out with physical methods, i.e. by the measuring apparatus itself, in the context of an absolute measurement. For practical purposes, radiance factor measurements are predominantly accomplished relative to commercially available reflection standards. In the present investigation, different widely used diffuse reflection materials were measured for the first time in a multi-geometry configuration with the robot-based gonioreflectometer of the Physikalisch-Technische Bundesanstalt (PTB) in order to characterize their three-dimensional reflection behaviour. For a set of four distinct incident angles, the full hemispherical reflection indicatrix was determined at a wavelength of 550 nm.The angle-resolved reflection data are an important reference for manufacturers, providers and users of radiometric and photometric products. This paper attempts to give users in research and industry an overview of the strongly non-Lambertian reflection behaviour of standard reflection materials, because it is a widespread false assumption that commonly used standard reflection materials have only minor deviations from the ideal specification of the PRD.

We used a flow cytometer together with an intensified CCD camera to record spatially resolved light scattering from micrometer-sized single particles and single oriented particle agglomerates. Experimental differential cross sections of an oriented dumbbell made from two identical polystyrene spheres were compared with theoretical values calculated within the discrete dipole approximation, and good agreement was achieved. Furthermore, characteristic two-dimensional patterns of the scattered-light intensity were recorded for single blood cells, yielding information on the cells' shape and volume. Besides flow cytometry, we observed and analyzed differential light scatter of particle clusters of known size, shape, and orientation located within an optical trap.

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At the Physikalisch-Technische Bundesanstalt, the National Metrology Institute of Germany, a new facility for measuring visual appearance-related quantities has been built up. The acronym ARGon(3) stands for "3D appearance robot-based gonioreflectometer". Compared to standard gonioreflectometers, there are two main new features within this setup. First, a photometric luminance camera with a spatial resolution of 28 μm on the device under test (DUT) enables spatially high-resolved measurements of luminance and color coordinates. Second, a line-scan CCD-camera mounted to a spectrometer provides measurements of the radiance factor, respectively the bidirectional reflectance distribution function, in full V(λ)-range (360 nm-830 nm) with arbitrary angles of irradiation and detection relative to the surface normal, on a time scale of about 2 min. First goniometric measurements of diffuse reflection within 3D-space above the DUT with subsequent colorimetric representation of the obtained data of special effect pigments based on the interference effect are presented.