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Integrating sphere (Ulbricht sphere)
The Ulbricht sphere is one of the most used equipment for measuring photometric quantities, especially in research laboratories; it is a hollow sphere with a perfectly diffusing internal surface that allows total reflection of the light, which can enter through a small slot.
As the sphere is made, the hole through which the light radiations pass is in effect a black body, which totally absorbs the incident radiation, without reflecting it.