The principle discussed involves the nature of light rays as they propagate from a source. Instead of spreading their energy uniformly across a vast area, light consists of discrete packets of energy known as quanta. These quanta are not divided but exist as whole units, which can be emitted or absorbed only in their entirety.

This concept reflects a fundamental shift in understanding light and energy, as proposed by Einstein. It emphasizes that energy operates in quantized forms rather than in a continuous manner, which has significant implications for the study of physics and our comprehension of light's behavior.