This presentation outlines the fundamental principles Solar Radiation applied to Agrivoltaics, a system designed to transform solar photons into two distinct commodities: electrical energy via photovoltaics and agricultural produce through crop photosynthesis. This presentation provides the basic principles of the physics of the Sun and how it generates photons. The presentation also examines how solar radiation interacts with the atmosphere through absorption, reflection, and scattering, while defining critical irradiance metrics such as Beam, Diffuse, and Global Horizontal Irradiance. Furthermore, the presentation covers solar geometry to calculate the sun's position, concluding with modeling strategies for "light sharing" that optimize effective irradiance for both PV configurations (tilted, vertical, or trackers) and crop yields.