integrating-sphere photometer[′int·ə‚grād·iŋ ‚sfir fə′täm·əd·ər]
a device that makes it possible to measure luminous flux with a single measurement. The primary assembly of an integrating-sphere photometer is an Uhlbricht sphere—a hollow sphere (or hollow body of a different shape) with the internal surface painted matte white. The diameter of the sphere must significantly exceed the dimensions of the light sources being measured. For example, integrating-sphere photometers up to 5 m in diameter are designed to measure the luminous fluxes of luminescent lamps. The illuminance of any point of the sphere that is shielded by a small screen from the direct rays of a light source within the sphere is proportional to the luminous flux of the source (or in the general case, to the radiation flux). The illuminance of the shielded area may be measured by any of several methods, for example, by means of a photoelectric device built into the sphere. Integrating-sphere photometers are used extensively in light and color measurements, particularly for measuring the luminous fluxes of lamps and luminaires, reflection coefficients, and transmission factors.