Ophir integrating spheres with detectors are calibrated over their specified spectral range. The IS-1 and 3A-IS models have an integral detector and the flexible IS6 offers several models with the optical sensor as an integral part of the system precisely calibrated together with the integrating sphere. The IS6 is also available uncalibrated for applications where the customer wants to use his own sensor and setup or does not need a sensor such as when using the sphere as a uniform light source. The integrating spheres are in general calibrated with a light source that is located far from the port so that it does not affect the reflective geometry of the sphere. When measuring a source of light that is located at or close to a sphere port, any reflective (or even partially reflective surfaces on the light source will contribute to the reflective surface area of the sphere, changing its calibration to read higher than it should. Therefore, light sources should be kept as far as practical from the sphere port and its surfaces should be as non-reflecting as possible. If this is not possible, see below.
For applications in which the source must be close to entrance port and the source has significant reflection, this will affect the accuracy of the measurement. For such cases, Ophir sells an auxiliary LED self-absorption calibration accessory to measure and cancel out this error.