What: Lighting the subject from one side so light reveals one plane and shadow another.
Why: Frontal light flattens; side light reveals the third dimension and texture.
How: Place the light source (a window) beside the subject at 45–90 degrees and watch volume emerge.
Common mistake: Shooting with direct flash so all shadow and volume vanish.
Exercise: Photograph the same face in frontal then side light and compare the sense of volume.