Whew. There are days when it's tough to reach the goal of a learning a day. This one came a bit late.
Subtractive Light: One of the most basic rules of shooting outdoors is "find the shade." And then stick your subject in it (especially if it happens to be human). It's surprising, of course, how often we forget to do that-- after all, the sunshine is lovely. But the reasoning behind the rule is simple: sunlight creates harsh shadows on the face-- the exception to which is near sunrise or sunset because the sun is both softer and the angle more "dead on." When you place your subject in the shade, the harsh shadows disappear, and the lighted area behind them glows. It's especially nice when the subject as dark hair. This is basically subtractive light theory in practice. You're subtracting sunlight.
What many people don't know is that even on overcast days it can be beneficial to move someone into the shade. When you study a face on an overcast day, you can still see dark areas under the eyes and chin; they're less severe, but often make the person look washed out and depressed. Move them into a "shaded" area, and the shadows disappear. More importantly, if you face them towards the open area, then you are shaping the existing light. The open area is now coming at them from the front rather than the top. Angle them and you create a subtle Loop light with a 2:1 ratio. What's wonderful about this is that you are essentially sculpting the sunlight.
The picture above was taken on a high overcast day with the subject sitting under a tree. His back is to it, and you can see the shadow that creates against the side of his face and underside of his arm. Because the tree is tall, the light is still able to press down upon him, pushing a shadow under his chin, and there is a highlight in his hair where the branches part.
My subject here is a business man in Papua New Guinea, a wonderful soft-spoken gentleman who's gentleness and wisdom is present in this photograph. Want to see something awesome? This was him the next day:
A totally different kind of wisdom at work.