A sample analyzer has an illuminator for illuminating an assay sample to cause luminescence, and a support for a sample vessel containing the assay sample. The support is adapted to position the assay sample proximate the illuminator. A detector is positioned along an optical axis extending from the illuminator, through the positioned assay sample, to the detector, so as to detect the luminescence from the assay sample. A reflector is removably disposed between the illuminator and the assay sample so as to reflect a portion of the luminescence back through the positioned assay sample toward the detector.