Integrating sphere
Integrating sphere turns up in 2 fields: lighting, paper optics. Here is what it means to the people in each one.
Integrating sphere in lighting
A white-lined hollow ball that spreads a source's light evenly so one detector can read its total lumens and color.
A sphere whose interior is coated with a highly reflective, matte white material, so light from a source inside bounces many times and spreads evenly over the wall. A detector or spectroradiometer port, shielded from direct light by a baffle, then reads a signal proportional to total flux. Spheres measure lumens, CCT, CRI and SPD quickly; corrections for the sample's own absorption use an auxiliary lamp. Large luminaires need large spheres or a goniophotometer.
"Put the sample in the 2 meter integrating sphere and run the auxiliary lamp correction, it's a dark housing."
Integrating sphere in paper optics
Hollow sphere lined with a highly reflective matte white that bathes a sample in diffuse light from all directions.
Light entering the sphere bounces many times off its white lining, typically barium sulfate or sintered PTFE, until it reaches the sample port from every direction at once. This produces the diffuse illumination that d/0 and d/8 instruments need for brightness, opacity and whiteness. Aging, yellowing or dirty linings shift readings, so sphere condition is one of the first suspects when a lab's numbers drift.
"Readings started wandering after the sphere got dusty, so service is coming out to clean and recoat it."