The optical properties of systems for protection against thermal radiation play a primary role in determining their effectiveness. An improved integrating sphere provides for determination of the average reflectance and transmittance of materials, each in a single measurement; this average is the correctly weighed average for the source. The sphere coating of pure aluminum oxide approaches the ideal of a perfectly diffuse reflectance, essentially constant over the wavelength range of interest with improved permanence. The somewhat low average reflectance of this coating also reduces the error due to nonuniform spectral response. Results obtained with this device and by other methods agree. This instrument is especially useful where the same source is used for measurement of optical properties and for exposure of materials to intense radiation.
John M. Davies and Walter Zagieboylo, "An Integrating Sphere System for Measuring Average Reflectance and Transmittance," Appl. Opt. 4, 167-174 (1965)