Integrating sphere

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An Integrating sphere is an optical component consisting of a hollow cavity with its interior coated for high diffuse reflectivity (i.e., white), having relatively small holes as needed for entrance and exit ports.

The shape of the cavity is commonly spherical, hence the name. Its relevant property is a uniform scattering or diffusing effect. Light rays incident on any point on the inner surface are, by multiple scattering reflections, distributed equally to all other such points and effects of the original direction of such light are minimized. An integrating sphere may be thought of as a diffuser which preserves power but destroys spatial information. It is typically used with some light source and a measurement instrument for optical power.

Integrating spheres are used for a variety of optical, photometric or radiometric measurements, such as:

quantifying the total of the light radiated in all directions from a lamp,
measuring diffuse reflectance of surfaces, while properly averaging over all angles of illumination and observation,
creating a light source with apparent intensity uniform over all positions within its circular aperture, and independent of direction except for the cosine function inherent to ideally diffuse radiating surfaces (Lambertian surfaces).
accurately measuring the sum of all the ambient light incident on a small circular aperture.
measuring the power in laser beam, with best available independence of beam details such as beam shape, incident direction, and incident position.