Note: In the days of candles, sailors were hired to run the rig
ging and lighting in the theater. The man taking care of the
candles often needed to remove one of the floating candles from
the moat to repair its guttering or to relight a candle that had
blown out. The sailor used a tool known as a “gaff” (a long metal
hook used to retrieve wayward ropes on sailing ships) to pull the
candles to the edge of the moat and to push them back out.
Thereafter, the man taking care of the lighting came to be known
as the gaffer. Strangely, as the technology in the theater advanced,
the gaff was cast aside, except for those occasions when an actor
needed to be violently removed from the stage with a hook, and
the term “gaffer” fell into disuse. But somehow, the term survived
in the film industry and today the head of the lighting department
is known as the gaffer.
In general, diffuse light is any light that has been scattered after leaving
the light source, or any light source that has a varying area of luminosity
or intensity. Scattering can be caused by atmospheric gases, clouds, or
reflection (bounce) off an uneven or rough surface. Any material that
causes parallel light rays to be scattered, bent, or reflected into
non-parallel paths is creating diffuseness in the light.
Figure 1.3 is an example of an image that is lit primarily by two dif-
fuse light sources.
Here on earth, all light has some measure of diffuseness. This is
because the light rays (or particles or waves if you wish to be picky) pass
through atmospheric gases, colliding with the gas molecules and shoot
ing in all directions. The most obvious example of this is the sky. Blue
light is scattered in the atmosphere much more than light at the red end
of the spectrum. This is because blue light has a much shorter wave
length than red light and is, therefore, scattered throughout the
atmosphere about ten times as much as red light. This scattering is what
makes the sky appear blue. Subsequently, the scattered blue light con
tinues omnidirectionally, some of which reaches the ground as diffuse
light. This bluish, diffused light can be seen in shadows on clear days.
Direct sunlight can also be diffused through clouds, colliding with water
droplets and continuing omnidirectionally. Cloudy days provide an excel
lent example of white diffused light. All the shadows on cloudy days are
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soft and diffused. Only the deepest crevices are likely to be very dark
since light is approaching from most directions but may not reach into
them. These dark areas where the light cannot reach are considered to
be “occluded” from the light. This is where the term “occlusion shad
ing” comes from.
Diffuseness can tell us much about the light source and the environ
ment. Direct light sources such as the sun, a candle flame, or a bare,
clear lightbulb produce nearly parallel light rays and fairly hard shadows.
But put a curtain, a lamp shade, or frosted glass in front of the source
and the light becomes diffuse, making shadows softer. Why does this
happen? Simply because when a small light source like a light filament
illuminates a translucent material like a lamp shade, the lamp shade
effectively changes the size of the light source. For example, a frosted
lightbulb seems to be a larger light source than a clear lightbulb, because
the light in the frosted lightbulb is “diffused” through the frosting.
Because the frosted lightbulb seems to be a larger light source, the
shadows it creates are generally softer. See more about soft shadows in
the “Size” section of this chapter.
Fluorescent sources are all diffuse sources. They all have a wide
area of luminosity (since they are frosted) that creates soft shadows
because the light appears to “wrap around” objects, creating an area of
shadow “falloff.”
The following two images are the same except that one is directly lit
by the sun and the other is diffusely lit by sunlight that has been diffused
through clouds. There is diffuse lighting in both images but direct light-
ing in only one of them.
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Figure 1.8: This image is nearly identical to the previous one, except
for the absence of direct lighting. As the contrast is lower, the softer
illumination and softer shadows are clearly visible.
Figure 1.7: Sharp shadows and higher contrast are visible in this
image, which has both diffuse and direct lighting sources (the sky
and the sun, respectively). The direct light overpowers the diffuse
light and diffused shadows.

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