Reflectance measurements of aluminium surfaces using integrating spheres

In the investigation of the considerable absorption of visible light in ind ustrially rolled aluminium surfaces, a thorough knowledge of the total refl ectance measurement method is required. In this paper a general introductio n to the integrating sphere method is given, with emphasis on the current u nderstanding of instrumental artefacts and ways of correcting them. Selecte d aluminium surfaces were measured employing two spheres; a single-beam ins trument equipped with a white-light source and a Si-photoelement detector, and a double-beam sphere, which measures reflectance properties with spectr al resolution. It was found necessary to take precautions concerning the or ientation of rolled samples relative instrument geometry, to avoid artifici al losses from the sphere. The use of a specular reference standard is assu med to minimise the effect of several sphere artefacts, since it produces s imilar angular distribution of reflected light as the rather glossy alumini um samples. Measurements with spectral resolution show that the total refle ctance of aluminium is somewhat red shifted after rolling, a tendency that cannot be revealed in ordinary white-light measurements. (C) 2000 Elsevier Science Ltd. All rights reserved.