Transmittance measurements in the integrating sphere.
The finite-difference equation method is used to derive expressions for the directional–hemispherical transmittance as measured in the integrating sphere; and for the correction factor necessary with a one-port sphere to account for changes in the enclosure caused by substituting the open port (the standard device) for the sample. Expressions are also derived for the hemispherical reflectance, since this quantity is necessary to compute the correction factor. It is also shown that no correction factor is necessary with a two-port (comparative) sphere.