Portraits can be formal or informal depending on what they're needed for. Formal portraits are almost always shot in the studio, where control over the lighting is a must, while informal portraits, or environmental portraits, as they are referred to, are mostly shot on location and show more of the surroundings, whether it be inside or outside. This enables the photographer to tell more of a story about that person.
When shooting with auxiliary lights on location, my lighting set ups are similar to what I do in the studio, but working with natural light is less predictable. To be successful in controlling natural light takes a lot of skill, since you're basically dealing with one thermonuclear light source, ninety three million miles away and redirecting it where you want it. This is achieved by introducing scrims, gobos, reflectors, fill flats and supplemental flash or hot lights to get the desired effect. The results should look natural in the final photograph.
Here is a selection of my favorite environmental portraits, shot on location, indoors and out.