This may be worth discussing in a future article. Objects are rendered with greatest realism when using a moderately diffuse source, such as an umbrella or light bank, because the smoothly flowing light and shade relationship depicts form with maximum clarity. This is the standard lighting set-up for all product photography in the slick catalogs that fill our mailboxes. Conversely, specular lighting distorts realism because its patterns of sharp shadows tend to visually compete with the actual form of the illuminated objects. Specular light also generates a form-distorting sharp line of demarcation between light and shade on a rounded object because the light rays are tangent to only a tiny portion of the curved surface.
Specular lighting is better suited to revealing textures on broad surfaces.
For example, we usually prefer a sunny day for scenics and architecture. Furniture catalogs use specular spotlights to highlight the textures and grain of their products. Many lamps are used with their placement meticulously controlled to avoid form-distorting overlapping effects. Furniture form is controlled not by lighting, but by careful placement to show perspective from the camera's point of view. Theatrical productions use specular lighting to direct our attention to specific areas of the stage.