Setting
up an Area Light
To see the
difference between the shadows cast by a single source light and
an area light, you can use a scene that has a strong back light
casting shadows into the foreground. The goal is to create shadows
that are attenuated as you get further away from the columns.
You can use
the following scene file to follow through the lesson steps.The
scene consists of four columns sitting on a plane with a single
point light behind the columns pointed in the general direction
of the camera. The light is a point light with its Attenuation
set to Physically Correct
and its Dimmer
value pumped up to about 33
to compensate.
Step
One: Test Render the Point Light
RMB-click on
the Render Launch button at the bottom of the viewer pane and select
the mantra1 output to render. You can see the resulting
sharp shadows being cast by the point light.

Step
Two: Turn the Light into an Area Light
Select the light
in the Network pane then in the Parameter pane, go to the Shading
tab. Set Area Shape
to Grid. Keep
the Size to
1 and the
Samples set
to 16.
Re-render the
image. Now the shadows are much softer with a clear attenuation
as the shadow moves away from the column. The shadows render with
a lot of noise which is a result of the low sample count used to
render this light. The number of samples can be increased at the
end after you are happy with the shape of the shadows. The light
has been distributed over the surface area as 16 separate sources
each with 1/16th of their original intensity.

Step
Three: Set the Area Size
Next, set the
Size to
3 while keeping the
Samples set
to 16. This
increases the spread of the shadows and further softens the lighting
effect.

Step
Four: Set the Area Samples
Next set the
samples to a higher value. This image used 2000 for maximum effect.
Once the samples have been increased then then the rendered image
appears more smooth. Obviously the longer render times produced
by the higher sample rates must be balanced with the level of quality
you require.

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