A mains electricity (AC-powered) laboratory instrument intended to be used to photometrically measure the optical absorbance or emission of clinical specimens in microplates containing multiple individual sample wells, with or without a separate cuvette-reading station. The device utilizes technology which may include reagent dispensing, a single or dual lightsource, bandpass filters, monochromators, photodetectors, data processing software and/or data displays to determine the qualitative and/or quantitative values of biological constituents of a clinical specimen. The device operates with reduced technician involvement and automation of some, but not all, procedural steps.