The relatively low cost of the daguerreotype in the middle of the 19th century and the reduced sitting time for the subject, though still much longer than now, led to a general rise in the popularity of portrait photography over painted portraiture. The style of these early works reflected the technical challenges associated with long exposure times and the painterly aesthetic of the time. Subjects were generally seated against plain backgrounds and lit with the soft light of an overhead window and whatever else could be reflected with mirrors.
When portrait photographs are composed and captured in a studio, the photographer has control over the lighting of the composition of the subject and can adjust direction and intensity of light. There are many ways to light a subject's face, but there are several common lighting plans which are easy enough to describe
Opposed to High-Key portraits, this technique is used only to highlight a specific part of the subject's face, often half of the face if only one light source is used or just the facial contour if two lights are used