Abstract: Agrivoltaic systems, as an emerging agricultural production mode, integrated photovoltaic power generation with agricultural cultivation and became an important pathway for achieving the “dual-carbon” goals by simultaneously ensuring clean energy output and agricultural productivity; however, the shading effects induced by photovoltaic (PV) modules often led to imbalances in the internal light environment, which reduced photosynthetic efficiency and crop yield and thereby constrained the synergistic benefits of agrivoltaic systems. To address this issue, this study took a PV agricultural installation supported by a 3.8 m-high steel structure in Guanyun County, Lianyungang City, Jiangsu Province, China, as a representative case and systematically investigated the regulatory mechanisms of different PV module layout configurations on the internal light environment throughout an entire year, as well as the associated spatiotemporal distribution characteristics of solar radiation. A parametric modeling framework was established using Rhino and Grasshopper, and annual light environment simulations were conducted with the Ladybug plugin, while field measurements of solar radiation were used to validate the accuracy of the simulation model. On this basis, the effects of PV module arrangement patterns and vertical projection ratio on the distributions of photosynthetically active radiation (PAR), light homogeneity index (X_LHI), and monthly average daily light integral (DLI) within the system were quantitatively analyzed. The results indicated that the vertical projection ratio was a key parameter governing both the total available radiation and the uniformity of light distribution within agrivoltaic systems, and reducing the vertical projection ratio from 43.7% to 29.2% increased internal PAR by 18.3%–38.5% while significantly improving light distribution uniformity, with the most pronounced enhancement observed during the summer season. In addition, PV module layout configuration exerted a notable influence on the internal light environment, as double-row arrangements exhibited superior light penetration and higher homogeneity compared with single-row configurations under the same projection ratio; specifically, when the longitudinal spacing between the two rows in a double-row structure was increased from 0 to 0.4 m, the summer X_LHI increased by up to 10.2%. Seasonal variation further intensified the spatial heterogeneity of light distribution, with irradiance levels in inter-row areas being markedly higher than those directly beneath the PV modules during summer and autumn, indicating that spatially differentiated planting strategies were more suitable for these seasons, whereas light distribution during winter and spring was relatively uniform, making unified cultivation of shade-tolerant or moderately light-demanding crops more appropriate. Overall, this study proposed a PV module layout design approach that integrated seasonal light distribution characteristics with crop light requirements, provided scientific support for structural layout optimization and planting mode design in agrivoltaic systems, and contributed to improved light use efficiency, enhanced agricultural productivity, and the coordinated development of photovoltaic power generation and agricultural production.