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aferrie
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- TL;DR Summary
- Are there any potential issues with measuring the reflectance of a non-planar object (e.g. a ball bearing or an insect specimen) using an integrating sphere?
I am designing an experiment to measure the reflectance (diffuse+specular) of insect specimens, and I plan to use an integrating sphere to collect the measurements. Typically, I have seen that reflectance measurements with integrating spheres are done with planar (i.e. flat) sample objects. So, I am curious if a non-planar sample object would produce an incorrect measurement.
My main concern is that the specular reflectance of the sample is now contained over a variety of angles, so orienting the sample at an 8deg incidence angle with respect to the source (as shown below) will not redirect all of the specular signal within the sphere. My proposed solution is to obtain a large integrating sphere so that the port fraction is low (i.e. around 0.3% assuming a port diameter of ~13mm and and integrating sphere diameter of 200mm). This will not eliminate all of the losses of the specular signal, but it will minimize them such that the reflectance measurement is accurate.
Image source
For reference, the reflectance measurement needs to be taken with each specimen fully illuminated.
My main concern is that the specular reflectance of the sample is now contained over a variety of angles, so orienting the sample at an 8deg incidence angle with respect to the source (as shown below) will not redirect all of the specular signal within the sphere. My proposed solution is to obtain a large integrating sphere so that the port fraction is low (i.e. around 0.3% assuming a port diameter of ~13mm and and integrating sphere diameter of 200mm). This will not eliminate all of the losses of the specular signal, but it will minimize them such that the reflectance measurement is accurate.
Image source
For reference, the reflectance measurement needs to be taken with each specimen fully illuminated.