What does light coming from the side do to a person's face or an object, making it look rounder and showing its shape better?

Side light, which illuminates a person's face or an object from the left or right, enhances its three-dimensional appearance by creating distinct areas of illumination and darkness. The parts of the face or object directly facing the light source are brightly lit, forming highlights, which are the brightest points of direct light. Conversely, the areas turned away from the light source or obstructed by other features receive less or no direct light, creating shadows. Between these highlights and shadows, there are gradual changes in brightness called mid-tones, where the light intensity smoothly diminishes across the curved surfaces of the object. This continuous gradation from light to dark, known as a tonal gradient, clearly defines the object's contours and curves. The contrast and smooth transition between these bright highlights, varying mid-tones, and deep shadows visually separate the illuminated side from the unilluminated side, giving the perception of depth, volume, and form. This process, termed modeling, makes the object appear rounder and reveals its three-dimensional shape and structure more effectively.