Seeing Light and Shadow
Lines create shapes: circles, squares, and triangles. When you add values in the correct places in the form of shadows and highlights, the geometric shapes take on the illusion of three dimensions. The thing that separates a flat circle from a round sphere is light and shadow. The key to adding dimension is understanding shadows.
The light that creates shadows and highlights comes from something: The sun, artificial light, a candle. The source of the light is called – surprise! – the light source. Pay attention to the light source when you’re drawing, especially when you’re indicating shadows. Multiple light sources are possible, but single light sources make for a more dramatic painting.
The highlights and shadows depend on whether the surface is shiny or dull – its reflectivity – the intensity of the light source, and the shape of the surface itself. The shadows and highlights on a flat surface, like a cube, are different than those on a curved surface, like a sphere or cylinder. But flat and curved surfaces are mostly light and shadow, and have few, if any, parts unaffected by the light source. The size of a shadow depends on the object and the light source.
All objects have some combination of highlights, reflected light, core shadows, cast shadows, and crevice dark:
Highlight: This is the area of lightest shadow. It’s where the light first strikes the shape and the closest point to the light source. The highlight follows the shape of the object. In the drawings in the following sections, notice the highlight is round on the sphere, a whole side plane on the cube and pyramid, and runs the length of the tube on the cylinder.
Reflected light: Light can bounce off other sources and land back on an object. If it bounces back or is reflected, the light is slightly dimmer than the original light.
Cast shadow: The object blocks light and casts a shadow where light is prevented from illuminating the surface upon which the object sits. The cast shadow changes shape with the angle of the light source and its distance from the object.
Experiment with a flashlight and a baseball to see the variety of oval cast shadows you can create. The cast shadow mirrors the object’s shape and follows the surface’s contours, if there are any (wrinkles in fabric or hills in snow).
The light source’s height and angle above the object determines how long the cast shadow is. If you’re outdoors, the sun is your light source, and the cast shadow will change by time of day. Shadows created by the sun are longer in the morning and evening, so a low angle of light elongates the shadows.
Core shadow: The darkest area of shadow is the place farthest from the light but without any reflected light bounced into it. The core shadow follows the contour of the shape. A sphere’s core shadow is crescent shaped, and a cylinder’s is a vertical flat strip along the tube.
Flat surfaces may not have a core shadow. Instead they may have a different value to each plane or side.
Crevice dark: The object sits on a surface, and where the object meets the surface is a line of deep dark shadow that I call the crevice dark, because a crevice is a deep narrow edge or opening that light can’t reach.