Hello everybody, i previously posted a topic about an exercise on luminance that was (appropriately, I admit) moved in the homework section. But nobody has still answered me. But the reason for which I didn't understand that exercise was that I was not sure about what luminance actually is, so I would like to understand it better. Can you help me? I've searched the Internet and asked my schoolmates (in this period i can't find the teachers) but nobody convinced me. I've read that luminance is the flux divided by the surface divided by the solid angle; but what does this exactly mean? In which way is luminance meant to be used? If i have a spherical lamp with uniform luminance in each of its points, indipendent of direction, and therefore the sphere is emitting isotropically, can I obtain the total luminous flux radiated by the sphere if I multiply the luminance by the total surface of the lamp and then by 2 pi (not 4 pi, because i suppose that the sphere is emitting only outside of its surface) ? Please don't move this topic, it is actually a theoretical question even if i don't know other way to express it than this exercise-like shape. Thank you in advance.