|Carl Spitzweg, "The Bookworm," 1850|
Capturing these effects while painting en plein air requires tremendous concentration and commitment. Once you see an effect that you want to capture, you have to paint it from memory and ignore other effects that strike your eye later.
Using a special eye light to spotlight the center of the face was common in film noir lighting.
Spotlighting can have powerful storytelling implications. In Gerome's "Death of Caesar," the body of the slain Caesar has already fallen into shadow, as if the light of history has moved on to his murderers and successors.
Gradating the edge of the spotlight effect makes it less obvious to the viewer, but it takes a careful organization of the palette if you want to paint it with opaques, because all of the colors of the scene must go through gradual transitions.
|Alphonse Mucha, "Nero Watching the Fire of Rome," 1887|
This also takes a lot of concentration: always to keep in mind the large statement, while you're fiddling with the details.
More about spotlighting in my book, Color and Light, available from Amazon (where it is still the #1 book on painting), and signed from my website (U.S. orders only).