Effects of integrating sphere conditions on the sphere uniformity

Integrating sphere is an important tool used in photometry and other optics-related fields to induce uniform scattering of a light source. An important property of an integrating sphere is its uniformity, which should be high so that the sphere provides smooth response. Necessary sphere components include a baffle and a photo-detector. However, the existence of the baffle is found to induce non-uniformity to the sphere response. Here we report an experimental study of the effects of integrating sphere components, especially the baffle, on its uniformity. In a typical condition, the response on the sphere wall opposite to the baffle was found to be lowered compared with that of the surrounding area, while that on the wall around the photo-detector behind the baffle was higher. Consequently, three baffle properties – reflectance of the baffle back surface, baffle size, and baffle position – were varied to see their effects on the sphere response, especially that at the sphere wall behind the baffle. It was found that the amplitude of the response of such area would be lowered regarding the following conditions: decrease in the reflectance of the baffle back surface, decrease in the baffle size, and increase in the distance between baffle and the detector. Adjusting these conditions yielded the lowered signals at such area and hence increasing sphere uniformity. However, the experiment showed that they also induced some adverse effects such as non-uniformity at other parts of the sphere. Thus these conditions should be optimised carefully in order to obtain the best uniformity.