Alzofon Art Institute Academy Lesson

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How Do You Do Shading?

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Definitions

To discuss shading, I am using a set of words with very particular meanings, which are defined here. Other publications may not agree with all my terminology...

...But I'm the one who's right.


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Definition Menu

Light Source

Secondary Light Source

Light (zone)

Halftone

Shade (zone)

Medium Light

Highlight

Low Light

Core of Shadow

Reflected Light (as a light source)

Cave

Cast Shadow


Light Source

The most luminous element affecting any given environment.

This might be, for example, the sun, or, if the sun is obscured by a cloudy overcast, then the overcast becomes the light source. The nature of the light source plays a critical role in form description.

Photograph of lamp mounted to ceiling, illuminating white plastic sheet.

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Secondary Light Source

Less luminous (than light source) elements affecting any given environment.

On a sunny day, the sky is a secondary light source to the sun. Highly reflective surfaces can act as secondary light sources. The influence of illumination from secondary light sources is important, but can never exceed the influence from the primary light source.

Photograph of lamp mounted to ceiling, illuminating white plastic sheet.
The plastic sheet is acting as a secondary light source, as it reflects illumination back to the ceiling.

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Light (zone)

The area on form which is receiving illumination from the light source. You can cast a shadow over the lit side of form.

While secondary light sources can illuminate shade zones, the contrast of intensely illuminated light zones precludes any part of the shade zone from being as light as any part of the light zone.
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Halftone

The area along the boundary between shade and light where there is a visible mix between shade and light.

Halftone is found only where textured form turns from light, and is not the edge of a cast shadow.

Because halftone contains light, you can cast a shadow over the halftone area.

Many people have trouble conceptualizing the halftone area, so I have made a page with much more detail about this area.

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Shade (zone)

Area where the light source cannot illuminate, due to form turning away, or to light blockage by a shadow casting body.

You cannot cast a shadow over the shade zone.

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Medium Light

Area on form receiving a greater level of illumination from light source.

For an explanation of the levels of illumination, click here.

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Highlight

A reflection, focused or diffuse, of the light source.

The reflection of the lamp is the highlight. Because the surface is very glossy, we see a reflection of the light source. An eggshell finish on the same surface would soften the focus to such an extent that you would not be able to identify the lamp anymore; but this area would contain the highlight just the same.

Photograph of lamp mounted to ceiling, illuminating white plastic sheet.
As the observer moves about, the highlight moves; while light from illumination is fixed. This is due to a basic rule about reflection, to be discussed later.

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Low Light

Area on form receiving a lesser level of illumination from light source.

For an explanation of the levels of illumination, click here.

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Core of Shadow

This is a compound effect:

  1. Within shade, due to the relative position of observer to an object in open space, some parts of form bounce less reflected light back into our eyes, thus appearing darker. Typically, this area will be a plane turned toward us.
  2. The second factor -- completing the definition -- is the presence of a lit side of the form. The illuminated side turns from the light, into the darkened plane facing you. All these factors work in concert to create the core of the shadow.
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Reflected Light (as a light source)

Reflected light acts as illumination from non-primary light sources.


Reflected light influences color or lightness level on all parts of the form, but its influence is most evident in the shade zone. Reflective surfaces illuminate nearby forms, even if weakly. As light sources, reflective surfaces cannot illuminate as strongly as the primary light source. The sky can be thought of as a reflective medium.

Photograph of lamp mounted to ceiling, illuminating white plastic sheet.
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Cave

Extreme recessions where, due to a closed configuration, light is prevented from reflecting back to your eye.

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Cast Shadow

Light rays travel in a straight-line path out from the source. Objects block light rays from continuing along this path.

Areas behind the light-blocking body will not be illuminated. These areas are said to have a shadow cast over them.

The boundary of a cast shadow can be plotted by running a straight line from the light source to the edge of the light blocking form, down to the next surface.

At the boundary of the shade zones, cast shadows have a different edge quality than halftones. Cast shadows have penumbras. Soon I will develop a section describing the nature of penumbras.

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Rebecca Alzofon can be e-mailed at rebecca@art.net
This page created October 9, 1996