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• THE FORM PRINCIPLE: The Form Principle is the rendering of form as to its aspect at any given moment with regard to its lighting, its structure and texture, together with its true relationship to its environment.
• The rendering of light on a form is the first way to present a convincing illusion of existing form. Without light, form ceases to exist. It must be determined at once what kind of light we are working with, for it's nature and quality and the direction from which it comes will affect the entire appearance of the form.
• If it is impossible to render form without light, then it follows that the nature of the form becomes visible because of light.
• A brilliant light produces well-defined light, halftone, and shadow.
•A diffused light (light of the sky on a grey day) produces an effect of softness and subtle gradation of light to dark.
• The direction or position of the light source determines what planes shall be in the light, halftone or shadow. Texture is more apparent in a direct or bright light than in a diffused light. The planes of the form are also more apparent in brilliant light.
• The lightest area of the form will be within those planes lying most nearly at right angles to the direction of the light. The halftone planes will be those obliquely situated to the direction of the light. The shadow planes will be those planes lying in or beyond the direction of light so that the light of the original source cannot reach them. The cast shadows are the results of the light having been intercepted, and the shape of such intercepting form is projected to other planes. In diffused light there is little or no cast shadow. In brilliant light or direct light there is always cast shadow.
• The kind of light immediately has to do with the approach to your subject. Diffused light has less definition and is more difficult. For "snap", take direct light. For softness and simplicity, use sky light. Direct light produces contrast, sky light produces closeness of value.
• Direct light produces much more reflected light, and this is most apparent within the shadow. The amount of reflected light reaching the shadow will determine its value. Everything upon which the light falls becomes a secondary source of reflected light and will light shadow planes in the same manner as the original source, being brightest on the planes at right angles to such reflected light.