Investigation of Opposition Effect in Integrating Spheres

Oetking has presented experimental evidence that the radiance reflected from magnesium oxide surfaces as well as most others tested increases markedly when the surface is viewed from within a few degrees of the direction of incidence. Because magnesium oxide is commonly used as a diffuse coating material in integrating spheres, a question arises regarding the error caused by this effect. This work examines the magnitude of the error introduced by neglecting the so-called “opposition effect” in the measurement of reflectance using integrating spheres and shows the error to be negligible.