Predictive algorithms for directional optical properties of coated glazing for building and automotive applications

Solar and visual light transmittance, colour appearance and other optical properties of glazing, are according to present standards specified for (near-) normal incidence. In general however, these properties are angular dependent. Realistic computation of visual light and solar energy properties therefore requires the angular behaviour to be known. The paper gives an overview of possible strategies for the development and use of algorithms for the prediction of the angular dependency of these properties. A new type of algorithm is proposed based on an 'exact' Fresnel model in which the complex Fresnel equations are replaced by more simple expressions. Different candidate expressions for this pseudo-Fresnel formalism are discussed and their results compared with the exact solution. The present work has been focused on the angular dependency of the visible light transmittance of a set of coated glazing materials which covers most of the products available today on the market. The results show that the new algorithm gives an accurate description of the angular behaviour of the optical properties of coated glazing for buildings and automotive applications. (C) 1999 Elsevier Science S.A. All rights reserved.