Systems are provided for a modular multi-wavelength UV-VIS detector unit, such as an absorbance detector (e.g., spectrophotometer) included in a high-performance liquid chromatography system. In one example, a detector unit includes one or more light emitters and a sliding assembly configured to slidingly move a flow cell relative to the one or more light emitters, the one or more light emitters mounted on a floating rig to facilitate alignment between the one or more light emitters and the flow cell when the sliding assembly is in a closed position.