A sample analyzer, comprising: an illuminator; a support positioned to support a sample vessel containing an assay sample proximate the illuminator, such that the illuminator causes luminescence of the assay sample; a detector positioned along an optical axis extending from the illuminator, through the assay sample, to the detector, so as to detect the luminescence of the assay sample; characterised by: a reflector removeably disposed between the illuminator and the assay sample, to reflect a portion of the luminescence back through the assay sample toward the detector, wherein the reflector is disposed on a shuttle, the shuttle moveable to align the reflector with and perpendicular to the optical axis and adjacent the assay sample during a measuring mode of analysis, and to remove the reflector from the optical axis during an illumination mode; and a light diffuser which is disposed on the shuttle, the shuttle moveable to align the light diffuser with, and perpendicular to, the optical axis and adjacent the assay sample during the illumination mode, and to distance the light diffuser from the optical axis and to align the reflector with, and perpendicular to, the optical axis and adjacent the positioned sample during the measuring mode. an illuminator; a support positioned to support a sample vessel containing an assay sample proximate the illuminator, such that the illuminator causes luminescence of the assay sample; a detector positioned along an optical axis extending from the illuminator, through the assay sample, to the detector, so as to detect the luminescence of the assay sample; characterised by: a reflector removeably disposed between the illuminator and the assay sample, to reflect a portion of the luminescence back through the assay sample toward the detector, wherein the reflector is disposed on a shuttle, the shuttle moveable to align the reflector with and perpendicular to the optical axis and adjacent the assay sample during a measuring mode of analysis, and to remove the reflector from the optical axis during an illumination mode; and a light diffuser which is disposed on the shuttle, the shuttle moveable to align the light diffuser with, and perpendicular to, the optical axis and adjacent the assay sample during the illumination mode, and to distance the light diffuser from the optical axis and to align the reflector with, and perpendicular to, the optical axis and adjacent the positioned sample during the measuring mode. a reflector removeably disposed between the illuminator and the assay sample, to reflect a portion of the luminescence back through the assay sample toward the detector, wherein the reflector is disposed on a shuttle, the shuttle moveable to align the reflector with and perpendicular to the optical axis and adjacent the assay sample during a measuring mode of analysis, and to remove the reflector from the optical axis during an illumination mode; and a light diffuser which is disposed on the shuttle, the shuttle moveable to align the light diffuser with, and perpendicular to, the optical axis and adjacent the assay sample during the illumination mode, and to distance the light diffuser from the optical axis and to align the reflector with, and perpendicular to, the optical axis and adjacent the positioned sample during the measuring mode.