Makes me think of the steradian. This is used in photometery for basic things like the lumen (1 lumen = 1 candela per steradian), where there's the concept of a

Makes me think of the steradian. This is used in photometery for basic things like the lumen (1 lumen = 1 candela per steradian), where there's the concept of a light source emitting in all directions uniformly, and also what amounts of that arrive at what distances onto a surface, and what amounts are absorbed or reflected, and so on. https://en.wikipedia.org/wiki/Steradian https://en.wikipedia.org/wiki/Steradian https://en.wikipedia.org/wiki/Lumen_(unit) https://en.wikipedia.org/wiki/Lumen_(unit)