This paper presents a model for the directional response of a real int
egrating sphere detector system. The directional response is shown to
depend on three factors: the transmittance of the entrance port, the d
irectional-hemispherical reflectance of the sphere wall coating, and a
factor describing the effect of topographical features on the sphere
wall. Analysis of the entrance-port edge effect is provided. Experimen
ts are reported that quantify these factors and verify the model for a
real integrating sphere detector system that is based on an actual co
mmercial integrating sphere.