As I do from time to time, this piece is what I think someone else meant to write, or ought to have written.
There is something to be said about the quality of light. Something other than a lot of technical detail about point sources and diffusion and falloff. You can just talk about how it looks, and you can just observe how it looks. I'm going to dig up some pictures. Note that the picture might be a result of manipulation (note especially the Smith!), it might look like one thing while in reality it was another, but we don't care. What we care about it what it looks like.
Look at these pictures. Note the character of the shadows -- deep black, or weak? Note the character of the shadow's edges -- Soft or sharp? Note the way the light falls off. Are lit surfaces farther from the main light source about as bright no matter where they are, or are the ones farther away more dimly lit, as if the light was small and up-close? Can you tell at a glance which ones are (or appear to be) sunlight and which are artificial light?
W. Eugene Smith. Three Soldiers.
Henri Cartier-Bresson. Behind the Gare St. Lazare.
Robert Demachy, Study IV.
And here we have a Weston.
Joseph R. Keiley, Portrait -- Miss de C.