A photometric calibrator is disclosed wherein a known and continuously vable amount of light flux received at a detector is linearly proportional to the inverse fourth power of the optical path length between the detector and a primary, quasi-point source of the light flux. The calibrator includes a secondary, quasi-point light flux source wherein the total flux emitted thereby is proportional to the flux received thereby over a quasi-point detecting area located at some distance, d, from the primary source. The detector is located at an equal distance d from the secondary source.
A luminometer is described comprising a tray for receiving an array of sample wells, a photodetector assembly, and means for relatively moving the tray and photodetector assembly in one direction to align the sample wells received by the tray in a predetermined sequence with the photodetector assembly. The photodetector assembly of the luminometer includes a stage, a photodetection head having a detection aperture permitting passage of light therethrough, a means for mounting the photodetection head to the stage that permits movement of the head in a direction substantially normal to the direction of relative tray and photodetector assembly movement, and a means for biasing the photodetection head toward a selected sample well so that the detection aperture is substantially isolated from light emitted from adjacent wells. Internal and external photodetector calibration systems and a sample heater are also contemplated.
