The repartition of the single reflections in an integrating sphere is discussed using a model sphere where wall and screen are divided into twenty-six zones. The results lead to a simplified model with three zones and three partial luminous fluxes. In this simplified model sphere, the net hold is defined as that part of the volume of the sphere that is hidden by the screen when one looks into the sphere through the sphere window. The optimal place and the optimal size of the screen are determined with assumption of a constant net hold. Then the screen is mainly given by the ratio between the diameter of the net hold and the observation window. Further influences will only slightly affect place and size of the screen.
F. Rotter, "View into the Integrating Sphere Through the Observation Window," Appl. Opt. 10, 2629-2638 (1971)