Interlaboratory comparison of solar range transmittance and reflectance of coated and uncoated flat glass

Abstract

Transmittance and reflectance measurements on glass for architectural applications using commercial spectrophotometers may be affected by errors resulting from an improperly operated instrument, an inappropriate calibration, etc. Discrepancies between the values of parameters such as light reflectance and solar factor measured on the same glass product by different laboratories can be very pronounced. In order to avoid disputes among glass producers and complaints from glass users the interlaboratory reproducibility and the accuracy of the measurements must be improved. A n intercomparison was organized by Technical Committee 10 "Optical Properties of Glass" of the International Commission on Glass among 15 laboratories and one metrological institute on transmittance and reflectance measurements on commercial coated and uncoated glasses. Good reproducibility and accuracy in transmittance measurements ( ± 0 . 6 %) have been achieved even with each laboratory using its own instrumental procedures. In the case of reflectance, a preliminary round robin performed using the same instruments gave very large discrepancies in the spectral and integrated values. Reproducibility and accuracy of the same order of magnitude as in the transmittance measurements were obtained when each laboratory used a standardized procedure and the same reference standards, the latter having optical characteristics similar to the samples.