How does the idea of radiance as energy moving along a ray capture the “per unit area” part of this definition?
What does "energy along a ray" mean? I'm having trouble understanding what radiance measures.
I am also struggling with how the angle relates to this. Is the intuition that more photons hit at a perpendicular angle rather than a non-perpendicular angle?
it is different from the radiant flux that this radiance is same on different distances?