Integrating Spheres, for Reflection and Irradiance Measurements

An integrating sphere works as a light collector, enabling use as a diffuse illumination or measurement source.

The basic principle is that light enters the sphere through the sample port, goes through multiple reflections on the highly reflective, Lambertian surface of the sphere and is scattered uniformly around the interior of the sphere. Behind a baffled port inside the sphere, which is independent of the angular properties of the sample port, a fibre optic cable collects a homogenised light signal and carries it to the spectrometer. The baffle is very significant as it prevents first reflections from entering the detection fibre.

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The AvaSphere series integrating spheres are available with active diameters of 30, 50 and 80mm and an SMA port at 90 degrees for collecting the irradiance and reflection signals.

The reflection spheres feature an additional SMA connector port angled at 8 degrees to the sample port, for direct illumination. This port couples external light into the sphere through a fibre optic cable connected to a collimating lens.

The sample port diameters are 6 mm for the AvaSphere-30, 10 mm for the AvaSphere-50 and 15 mm for the AvaSphere-80. All sample ports are knife-edge, ensuring a near 180 degree field of view of the sample port.

The irradiance version of the integrating sphere can be used for measurements of light sources, such as lasers, LEDs and incandenscent sources.

For irradiance measurements of 5 mm cylindrical LEDs, a special adapter is available for the AvaSphere-50/80-IRRAD. This adapter ensures correct and reproducible positioning of the LEDs inside the sphere.

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The AvaSphere reflection version is used for the measurement of total integrated reflectance of a surface, as well as for colour measurements and fluorescence spectroscopy on solids/powders. The principle of measurement is based on direct illumination and indirect reflection. The AvaSphere-50-LS-HAL with internal light source can be a used as a low-cost uniform source and is available with an intensity calibration file.

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The inside of the integrating spheres is made of a highly reflective diffuse PTFE material. This provides over 96% reflectance over a wide wavelength range of 250-2500 nm.

For the AvaSphere-50-REFL, a special black gloss trap is available to exclude specular reflection in the measurement. Please order this option when ordering the sphere. In case specular reflection needs to be included, a white reflective part, which is standard on the AvaSphere-50-REFL, can be mounted in the position of the gloss-trap.

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For applications that require much stronger illumination, we offer a version of the  50mm sphere that has an integrated Halogen light source, the AvaSphere-50-LS-HAL. This integrating sphere provides up to 160x more light on your sample for a reflection measurement when compared the standard 50mm version. The sphere provides diffused halogen light on your sample without the losses typically experienced with fibre optic coupling, and has a direct collimated SMA port for collection of the reflection signal with any of our AvaSpec spectrometers.

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It’s mostly useful for dark or low reflecting materials and NIR spectral measurements where signal strength can be limited. It is also very useful for measuring gem stones. In the application section of this website, a complete gemology setup can be found.

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The AvaSphere-50-LS-HAL-12V has an internal diameter of 50mm, a sample port of 10mm and an SMA terminated reference port. The 5W halogen lamp is stabilised and cooled with forced airflow, and supplied complete with a 12V power supply. The switch line makes it possible to remotely switch the ligthsource on/off with a TTL signal.