Light Logic and the Rendering of Three
Dimensional Objects onto a Two Dimensional
Surface.
You will make your art more believable when you keep these basics in mind
A Light Source and Shadows
A light projected onto an object or figure creates lights, darks, and cast shadows. Your
source of light may be the sun, the moon, a light through a window or an artificial light.
When several light sources are present the light and dark tones vary and are less
predictable. To simplify the study of light and shadow in this first section, I will use only
one light source.
Two Kinds of Shadows
There are two kinds of shadows that occur when one light shines on an object, a cast
shadow and a form shadow.
Cast Shadow
When an object blocks a light source it casts a shadow. A cast shadow is not a solid
shape but varies in tone and value. The farther a cast shadow is from the object which
casts it the lighter and softer and less defined becomes its edges.
Form Shadow
A form shadow is the less defined dark side on an object not facing the light source. A
form shadow has softer less defined edges than a cast shadow. Form shadows are
subtle shadows essential for creating the illusion of volume, mass and depth. The
changes in form shadows require careful observation - quinting at the subject to see
value definition affected by figure-ground making value relationships clearer.
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A Light Side and a Dark Side on Round or Circular Surfaces
When one light source is present, I was taught the dark side is "always" darker than the
light side of the object and the light side is "always" lighter than the dark side.
Establishing a definite light side and dark side makes round objects appear round and
defines the form of an object accurately
Li9ht
Mli:ldle
Tone
THE LIGHT SIDE IN TWO PARTS
Highlight
The lightest spot or streak is where the light strikes the subject in exactly the middle of
the light side between the shadow edge and the edge of the object. A highlight can be
shinny and crisp on a glass or metallic surface, or fuzzy and muted on a dull or textured
surface.
Light middle tones
Note, to avoid confusion, "always" keep the values on the light side lighter than the
values on the dark side. In reverse, the values on the dark side are darker than the
values on the light side. It's the middle tones on either side that confuse the artist's eye
in value relationships.
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The Dark Side in Three Parts
Form Shadow in Three Parts
"Shadow edge" or "core shadow"
The edge where the light is blocked from the light source is the darkest value on the
dark side. The core or darkest value blends into the middle tones from the shadow
edge on round subjects.
Dark middle tone
The variable values blended form the shadow edge on the dark side. Again, the dark
middle tones are darker than any values on the light side. The human eye can trick the
brain into believing the
lightest values on the dark side are the same as the darkest values on the light side. If
the artist is confused about lights and darks, the rendering is less understandable.
Reflected light
If the object being painted is sitting on a white table, the light from the table reflects back
onto the object and makes the shadow side lighter. If the object of the painting is resting
by something black or dark, the middle values will become a dark reflection. The
concept also holds true when the object of the painting is sitting on a colored surface.
Cast Shadows
When the source of light is blocked by an object it casts a shadow. The length and
shape of the cast shadow depends on the placement of the light source. Long shadows
are cast from a side light source (as from the sun in late afternoon or early evening),
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and short cast shadows are cast from overhead (as from a noonday sun). The shape a
shadow casts depends on the shape of the object casting it and how closource is to the
object.
CAST SHADOWS IN THREE PARTS
The vocabulary used to describe cast shadows in art come from shadow descriptions in
astronomy. The umbra, penumbra and antumbra are the three distinct names given to
the description of shadows cast by heavenly bodies. The umbra is the darkest part of a
shadow considered the absence of light. The penumbra is a lighter outer shadow where
the object is only partially obscuring the light. The antumbra is more obscure. When it is
visible it seems to extend out from the penumbra in a lighter and less distinct way.
Li9ht~---Source
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Light Source, Cast Shadows and the Axis
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The Oidanc:e of a light
Source
The distance of on objed 'rom the ~ght source
light side and do rk side of the ebject,
The Axis Divides
affads
the appearance
of the
the Light Sid. from the Dark Sid.
Using the sphere as an example,
the light side and dot« IIde of tt... spher.
(on b. separated
by drawing
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oxls hn. showing the division between
the
two. The axis also d.flnes
the angle from which the Ught II (omlng.
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A Cone of light
A light SOUKa dose to on obi.d, such as a lamp,
prolectl 0 "Cone of lIgltt" or the light redtetes
In the
shape of a cene, The doserthe
light source II to the
sphere the nearer the axis dividing tho light side
from the dark ude will b. to the light source. ThIs
wilt caUle the light Iide to appear
smaller than the
dart.: lido. The farther the light source Is from the
sphere the mare centered
the axil becomes.
Light From a Distanu
Appears in Parall.1 Line.
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