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AutoCAD and Its Applications—Advanced
Copyright Goodheart-Willcox Co., Inc.
Attenuation
The farther an object is from a point light or spotlight, the less light that reaches
the object. See Figure 17-4. The intensity of light decreases over distance. This decrease
is called attenuation. All lights in AutoCAD, except distant lights, have some kind of
attenuation. Often, attenuation is called falloff or decay. However, do not confuse this
with the falloff of a spotlight, which is the outer edge of the cone of illumination. The
following attenuation types are available in AutoCAD point lights and spotlights.
• None. Applies the same light intensity regardless of distance. In other words,
no attenuation is calculated.
•
Inverse
Linear. The illumination of an object decreases in inverse proportion to
the distance. For example, if an object is two units from the light, it receives 1/2
of the full light. If the object is four units away, it receives 1/4 of the full light.
•
Inverse
Squared. The illumination of an object decreases in inverse proportion
to the square of the distance. For example, if an object is two units from the
light, it receives (1/2)2, or 1/4, of the full light. If the object is four units away,
it receives (1/4)2, or 1/16, of the full light. As you can see, attenuation is greater
for each unit of distance with the
Inverse Squared
option than with the
Inverse
Linear
option.
PROFESSIONAL TIP PROFESSIONAL TIP
The intensity of the sun’s rays does not diminish from one point on
Earth to another. They are weakened by the angle at which they strike
Earth. Therefore, since distant lights are similar to the sun, attenua-
tion is not a factor with distant lights.
Less
illumination
More
illumination
Attenuation
Figure 17-4.
Attenuation is the intensity of light decreasing over distance. Attenuation has been turned on
in this scene.