ON MEASUREMENT TECHNIQUES FOR THE SPECTRAL ABSORPTANCE OF GLAZING MATERIALS IN THE SOLAR RANGE

Advanced glazing materials may be thick, scattering, and inhomogeneous , and this poses problems for conventional absorptance measurement tec hniques. This paper describes a technique for accurately measuring the spectral absorptance of such materials. The measurement technique, in which the sample is mounted at the centre of an integrating sphere, w as analysed and the errors that occur when applying the technique to l arge samples were analysed. The technique was used to measure absorpta nce of several materials, and the results are presented. For heterogen eous materials it is necessary to irradiate a relatively large area to get a representative sample. It was found that under certain conditio ns (depending on the sample absorptance), sample sizes as large as 30% of the sphere diameter can be used without incurring a prohibitively large error. This paper examines the effect of the finite absorptance of the rod supporting the sample, showing that it can be important unl ess certain precautions are taken. (C) 1998 Elsevier Science Ltd. All rights reserved.