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<H1><A ID="SECTION00600000000000000000">
Light Sources</A>
</H1>
<P>
The lighting in a scene is determined by the number, type, and nature
of the light sources defined in the input file. Available light sources
range from simple directional sources to more realistic but computationally
costly quadrilateral area light sources. Typically, you will want to use
point or directional light sources while developing images. When
final renderings are made, these simple light sources may be replaced by
the more complex ones.
<P>
No matter what kind of light source you use, you will need to
specify its intensity.
In this chapter, an <#266#><EM>Intensity</EM><#266#> is either a red-green-blue triple
indicating the color of the light source, or a single value that is
interpreted as the intensity of a ``white'' light.
In the current version of <#267#><#1809#><EM>rayshade</EM><#1809#><#267#>, the intensity of a light does
not decrease as
one moves farther from it.
<P>
If you do not define a light source, <#268#><#1811#><EM>rayshade</EM><#1811#><#268#> will create a directional
light source of intensity 1.0 defined by the vector (1., -1., 1.).
This default light source is designed to work well when default
viewing parameters and surface values are being used.
<P>
You may define any number of light sources, but keep in mind that
it will require more time to render images that include many
light sources. It should also be noted that the light sources themselves
will not appear in the image, even if they are placed in frame.
<P>