Parameters
Pin : input power illuminating the integrating sphere
Ssph : area of the integrating sphere
nonDif : ratio of the non diffusing area over the integrating sphere area (the non diffusing area includes the eventual aperture through which the light illuminates the integrating sphere or from which the light exits from the integrating sphere or any aperture used to receive a detector or any eventual obscuration...)
Ref : albedo of the integrating sphere
Er : irradiance on the integrating sphere
Lr : radiance of the integrating sphere
