The Hamamatsu R11410 and R8520 photomultipliers (PMTs) are designed for applications in xenon-based dark matter detectors, featuring sensitivity to VUV light and stable operability at cryogenic temperatures. For eleven R11410 and seven R8520 PMTs, the relative photo-detection sensitivity at 470 nm was measured as a function of the position of the incident light on the photocathode. Typical non-uniformity values, considering 80 % of the photocathode surfaces, are 5 % - 10 % and 25 % - 30 % for the R11410 and R8520 types, respectively. It was found that the non-uniformity in the inner region of the photocathode is dominated by light reflections on the inner parts of the photosensors and the border regions contribute most to the observed non-uniformity.
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