During 1949-1955, researchers established the central role of pigment–protein antenna systems in capturing light energy and funneling it toward reaction centers, forming a coherent framework for how photosystems assemble and function. Parallel developments demonstrated that chloroplasts could drive photosynthesis in isolated preparations, enabling controlled biochemical dissection of light-driven processes. The emerging picture linked structural organization of pigment complexes with the onset of carbon fixation, setting the stage for later integration of energy-harvesting and carbon-reduction pathways. Historical Significance: These advances unified energy capture with initial carbon-flow understanding, marking a shift from organism-level observations to mechanistic models of photosynthesis and laying the groundwork for the sophisticated photosystem concepts that later dominated the field.