The present disclosure provides apparatus, systems and method for detecting separately and substantially simultaneously light emissions from a plurality of localized light-emitting analytes. A system according to exemplary embodiments of the present disclosure comprises a sample holder having structures formed thereon for spatially separating and constraining a plurality of light-emitting analytes each having a single nucleic acid molecule or a single nucleic acid polymerizing enzyme, a light source configured to illuminate the sample holder, an optical assembly configured to collect and detect separately and substantially simultaneously light emissions associated with the plurality of light emitting analytes. The system may further include a computer system configured to analyze the light emissions to determine the structures or properties of a target nucleic acid molecule associated with each analyte.