As you move farther from a light source, what does the photon spread over?

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When moving farther from a light source, the photons emitted from that source spread out over a larger area. This phenomenon is primarily due to the inverse square law, which states that the intensity of light (and thus the number of photons per unit area) decreases as the distance from the source increases.

As you double the distance away from the light source, the photons have to cover an area that is four times larger because the area of a sphere increases with the square of the radius. Consequently, even though the total number of photons might remain constant, the density (or concentration) of those photons per unit area diminishes, resulting in a larger surface area being illuminated as you move away.

This concept is crucial in understanding light propagation and how we perceive light intensity at different distances from the source. It explains why objects appear dimmer the farther they are from a light source, despite the constant emission of photons.