2009

as bright. A negative value subtracts light and thus is useful for selectively
placing dark areas in the scene. Default=1.0.
Using this parameter to increase intensity can cause colors to appear "burned
out." It can also generate colors not usable in videos. In general, leave Multiplier
set to its default of 1.0 except for special effects and special cases.
High Multiplier values wash out colors. For example, if you set a spotlight to
be red but then increase its Multiplier to 10, the light is white in the hotspot
and red only in the falloff area, where the Multiplier isn't applied.
Negative Multiplier values result in "dark light." That is, the light darkens
objects instead of illuminating them.
Color Swatch Shows the color of the light. Clicking the color swatch displays
the
Color Selector on page 391 so you can choose a color for the light.
Decay group
Decay is an additional way to make a light's intensity reduce over distance.
Type Sets the type of decay to use. There are three types to choose from.
■ None (The default.) Applies no decay. The light maintains full strength
from its source to infinity, unless you turn on far attenuation.
■ Inverse Applies inverse decay. The formula is luminance=R0 /R, where
R0 is the radial source of the light if no attenuation is used, or the Near
End value of the light if attenuation is used. R is the radial distance of the
illuminated surface from R0.
■ Inverse Square Applies inverse-square decay. The formula for this is (R0
/R)2. This is actually the "real-world" decay of light, but you might find it
too dim in the world of computer graphics.
This is the decay formula used by
photometric lights on page 5005.
TIP If Inverse Square decay makes the scene too dim, you can try using the
Environment Panel on page 6689 to increase the Global Lighting Level value.
The point at which decay begins depends on whether or not you use
attenuation:
■ With no attenuation, decay begins at the source of the light.
■ With near attenuation, the decay begins at the Near End position.
Once the beginning point is established, the decay follows its formula to
infinity, or until the light itself is cut off by the Far End distance. In other
5086 | Chapter 18 Lights and Cameras