The calculation of heat gain through windows relies heavily on the data of glass radiative properties. With the widespread application of tinted and coated glasses in modern structures, as well as the increasing use of glass in double-glazed units, the reflection, emission and transmission characteristics of glass become a complicated problem and cannot be predicted with simple reasoning. On the other hand, an exhaustive measurement of glass radiative properties covering a broad range of wavelengths. incidence angles and for a double-glazed unit various surface combinations can be prohibitively expensive as well as time-consuming.

In actuality the experimental measurement can be supplemented by a theoretical prediction which promises to be more versatile and has a precision level only limited by the material's specifications and the optical constants used. Modern advances in the radiative transfer theory and the thin film optics have provided input to formulate equations and to predict thermal radiative properties of a wide variety of glass. Inspired by this fact. this paper was written in an attempt to present such equations and collect the relevant data useful for the calculation. It is hoped that with the help of the following information, the unmanageable experimental program can be significantly curtailed while still yielding property values adequate for engineering practice.