For simplification, let's have a source light for a map projection.
I know where to put the source light in order to get an orthographic, stereographic, gnomonic map projection, but I still don't understand, for example, what the difference geometrically (where you put the light and how to project) between the equal-area projection and conformal projection is?
In other words, what and how to make a projection equal-area and the other conformal?