Effects of air mass and integration methods on results for optical property measurements of solar cover plate and absorber materials

Methods of calculating the transmittance of cover plate materials and the reflectance of absorber materials are compared. Optical data were obtained for both aged and unaged test specimens using an integrating sphere spectrophotometer. The data were integrated using both the weighted and selected ordinate methods in ASTM E 424, Method A, at air mass 2.0, and the selected ordinate method at air mass 1.5 and 1.0. The solar reflectance and solar transmittance values calculated using the various methods are presented and the impact of the data in terms of possible revisions to ASTM E 424 is discussed.