High Accuracy Measurements of Standard Reflection Materials and Goniochromatic Effect Pigments

Metrological Instrumentation

The basis for the description of diffuse reflecting materials is the concept of the radiance factor or as a quite similar depiction the bi-directional distribution function (BRDF). Both characterisations use the concept of the perfectly reflecting diffuser (PRD), which reflects by definition the incoming radiation loss-free, completely diffuse and with a Lambertian direction characteristics. The PRD is a theoretical concept only, which cannot be realised materially. Since there is no material with these characteristics, the realisation 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 accomplished predominantly relative to commercial available reflection standards.

The aim of this work will be the measurement of different, widely used diffuse reflection materials in multi-geometry configuration with the robot-based gonioreflectometer of the Physikalisch-Technische Bundesanstalt (PTB) in order to characterize for the first time their three-dimensional reflection behaviour. The work includes spectrally and also spatially resolved measurements with different types of detector systems like single element detectors, a line scan CCD-camera and a luminance video photometer. These multi-dimensional spectrally and spatially resolved reflection data are an important reference for manufacturers, providers and users of radiometric and photometric products. Furthermore, the relation between the (microscopic) structure of the materials and their (macroscopic) reflection behaviour shall be investigated.

Ph.D. student: 
Wiegner (née Atamas)