Openings where light can exit or enter, normally called ports, that are used for detectors and sources must be small, less than about 5% of the surface area of the sphere, for the theoretical assumptions to be valid.
Openings where light can exit or enter, used for detectors and sources, are normally called ports. The total area of all ports must be small, less than about 5% of the surface area of the sphere, for the theoretical assumptions to be valid.