Measurement and prediction of angle-dependent optical properties of coatedglass products: results of an inter-laboratory comparison of spectral transmittance and reflectance

The European Union ADOPT project has been concerned with the accurate deter mination of the optical properties of coated glass products, describing rel iable procedures for angle-dependent measurements and the development of pr edictive algorithms to enable accurate angle-dependent performance characte risation based upon near-normal values only. An essential element of the AD OPT project was the inter-laboratory comparison of transmittance and reflec tance measurements for commercially available glazings. Thirteen European a nd three USA laboratories participated. The selected samples represent majo r categories of coated glass products used in buildings, Each participant r eceived a set of samples and measured the angle-dependent spectral transmit tance and reflectance under appropriate polarisation conditions for inciden t wavelengths within the solar spectral distribution. Calibrated mirrors we re also provided for reference purposes. This paper presents the results of the inter-comparison which show that near-normal solar, visible and spectr al transmittance and reflectance can be measured with an uncertainty of bet ter than +/-0.02, The inter-comparison illustrates the difficulties still e xperienced in making accurate oblique incidence measurements. The predictiv e algorithms, which require near-normal input data only, are capable of pre dicting the angle-dependent transmittance, reflectance and total solar ener gy transmittance for double and triple glazed windows to an accuracy which enables reliable calculation of the annual solar heat gain through windows, (C) 2001 Elsevier Science B.V. All rights reserved.