Abstract: To increase the direct light received by the detector and decrease reflections from the detection component support structures, the luminescent substance is placed as close to the detector as possible. More specifically, the apparatus is configured so as to slide out a structure shielding the detector from light and at the same time slide in the vessel containing the luminescent substance therein until the vessel comes right under the detector. The invention can detect trace luminescence from a small-volume sample by maximizing the amount of direct light received from the sample and minimizing the decay of indirect light received from the sample attributable to interactions with the vessel for containing the sample therein, the structure for collecting light, and the structure for supporting other detection components.