integrating sphere

hollow sphere, the interior of which is formed from, or coated with, a diffusely-reflecting material that is as spectrally non-selective and as spatially uniform as possible

Equivalent terms: "photometer sphere", "Ulbricht sphere"

NOTE 1 Owing to the internal reflections within the sphere, the illuminance on any part of the inside surface of the sphere for which the direct flux is hidden is theoretically proportional to the luminous flux entering the sphere, or produced inside the sphere by a lamp. The illuminance of the internal sphere wall can be measured via a small window.

NOTE 2 The window of an integrating sphere is often used in radiometric measurement systems to provide a source with good spatial uniformity and with an angular distribution of radiance or luminance that is close to Lambert's cosine law.

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