Complex sentence: Because such radiation expands as it passes through space, and as its energy is conserved (in vacuum), the intensity of all types of radiation from a point source follows an inverse-square law in relation to the distance from its source.
Split into simpler sentences: Because such radiation expands as it passes through space, and as its energy is conserved (in vacuum). The intensity of all types of radiation from a point source follows an inverse-square law in relation to the distance from its source.