Which type of lighting is essential for modeling the subject and defining form?

Main light is essential for modeling the subject and defining form because it serves as the primary source of illumination in a scene. This type of lighting is typically positioned to create highlights and shadows that reveal the contours and details of the subject, thereby enhancing its three-dimensionality. Effective use of main light allows for a clearer depiction of shapes, textures, and overall visual interest.

Accent light, while useful for highlighting particular features or creating dramatic effects, is not focused on modeling the overall form of the subject. Fill light is designed to soften shadows created by the main light and to evenly illuminate the subject, but it lacks the intensity and direction needed to define form effectively. Background light is employed to illuminate the backdrop of a scene, contributing to the depth and separation of the subject from the background, but does not serve the purpose of modeling the subject itself.