A reference material with close to Lambertian reflectance and fluorescence emission profiles

Fluorescent brightening agents are widely used in various industries to enhance the appearance of materials. The angular profiles of emission and reflectance of fluorescent surfaces have been shown to deviate from Lambertian behaviour, however, in industry and calibration facilities single geometry measurements are often used, which requires assumptions to be made on the angular distributions. In addition, the angular distribution of reflectance has been shown to deviate from that of fluorescence. In this work, it is shown that the angular distribution of reflectance is dependent on the excitation wavelength and the effect is explained by qualitative and quantitative models. These angular and spectral effects may cause measurement errors when single geometry bidirectional measurements are carried out. The angular distributions can be taken into account by using goniometrical measurements, which however, result in increased calibration time and cost. Alternatively, a reference material could be used where the angular dependencies are minimised. In this work, a novel material is presented which demonstrates more Lambertian emission and reflectance profiles than conventional polytetrafluoroethylene (PTFE) based materials and a smaller dependence of angular reflectance on the absorbance of the sample.