There are five kinds of light — and their corresponding kinds of shade — that tend to fit almost all the light conditions that we are likely to draw or paint: single-source light; double-source light; flat, diffused light; moonlight; and sculptural light.
1 Single-Source light
The simplest kind of light comes from a single source, such as the bright light of the sun, in the late morning, at midday, or in the early afternoon.
This single-source light- or direct light- may also occur in an interior setting, where there is a bright, artificial light coming from a fairly high, overhead source. Whatever the season or time of day, and whatever the setting, indoors or outdoors, the net effect is a bright light with a correspondingly deep, sharp-edged shadow. Thus, direct, single-source light can also mean bright light illumination by photo flash, fluorescent tube, flame, fireworks, dynamite, lightning, and so forth.
2 Double-Source Light
The second type of light and shade is a combination of two light sources: strong, direct light from one source; and a secondary, lesser light from some opposite source, away from the strong, primary light source. Thus, we now have major and minor light, or direct and indirect light. And this kind of light and shade can occur either outdoors or indoors, whether the light source is natural or artificial.
3 Flat, Diffused Light
Flat, diffused light occurs on overcast days, beneath cloudy skies, and tends to be cool, cheerless, and dreary, rather than bright, warm, and sunny. Indoors, such light has a screened, low intensity, averted character. There is a tendency toward overall shadow in this low key, moody light, projecting solemnity and melancholy.
4 Moonlight-single and double source
Moonlight is essentially single-source light – for example, a clear sky with a bright moon illuminating a wide, unobstructed space. But moonlight in a closed or restricted space-a lane surrounded by trees, a city street, or an outdoor passageway – may be reflected or bounced from various surfaces. Thus, we may have the direct, primary light of the moon and the indirect, secondary, reflected light. In moonlight, the environment is generally dark; shadows and silhouettes preponderate. It is also important to remember that moonlight is, in itself, reflected light-light received from the sun and then reflected off the surface of the moon. Thus, moonlight cannot be as bright as anything that gives off light from its own internal combustion, such as a torch, or even a mach. The light of the moon is cool and silvery.
5 Sculptural Light
This light type is one of the most interesting and compelling ways to define form. It is not a light that you actually see, but an arbitrary light that you invent to explore every aspect of the form, explaining everything, leaving out nothing. It is tempting to call this tactile light because you run the light over every turn and detail of the form. And like a fingertip, the light feels and records every detail of its volume. The light starts at the front of every form, then grows fainter as the form turns away from the light and recedes into darkness. Thus, the centres of the forms are brightly lit, while the edges turn away into shadow. It assumes a middling-bright, daytime light source. And the lights and shadows are invented quite arbitrarily for maximum comprehension.
Source/Credits: Dynamic Light and Shade by Burne Hogarth, Watson Guptill, New York, 1981