8

mental ray Light Shader Rollout 1189
AtthedefaultvalueofNone,theenergydoesn’t
decay, and photons can provide indirect
illumination throughout the scene.
At the value of Inverse, the energy decays
proportionally to its distance from the light. That
is, a photon’s energy is 1/r, where r is the distance
from the light source.
AtthevalueofInverseSquare,theenergydecaysat
an inverse square rate. That is, a photon’s energy is
theinverseofthesquareofthedistance(
r) from
the light source (
1/r
2
) .
In the real world, lig ht decays at an inverse square
rate, but this gives str ictly realistic results only
if you provide a realistic value for the energy of
the light. The None and Inverse options help you
adjust indirect illumination without worrying
about ph ysical accuracy.
Caustic Photons—Sets the number of photons
emitted by the light for use in caustics. This
is the number of photons in the
photon map
(page 3–1088)
used for caustics. Increasing
this value increases the accuracy of caustics,
butalsoincreasestheamountofmemoryused
and the length of render time. Decreasing this
value i mproves memory usage and render time,
and can b e useful for previewing caustic effects.
Default=10000.
GI Ph otons —Sets the number of photons emitted
by the light for use in global illumination. This is
the number of photons in the photon map used
for global i llumination. Increasing this value
increases the accuracy of global illumination, but
also increases the amount of memory used and
the length of render time. Decreasing this value
improves memory usage and render time, and
can be useful for preview ing global-illuminat ion
effects. Default=10000.
mental ray Light Shader R ollout
Select a light. > Modify panel > m ental ray Light Shader
rollout
Note: This rollout does not appear unless you have
enabled the mental ray ex tensions by using the mental
ray Preferences panel. In addition, the mental ray renderer
must be the currently active rende rer.
Note: This rollout does not appear on the Create
panel.
The mental ray Light Shader rollout lets you add
mental ray shaders (page 2–1520) to lights. When
you render with the
mental ray renderer (page
3–77)
, light shaders can alter or adjust the light’ s
effect.
To adjust the settings for a light shader, drag the
shader’s button to an unused Material Editor
sample slot.
Be sure to choose Instance when
prompted to use an instance or a copy. (If you
edit a copy of the shader, you wi l l have to drag the
sample slot back to the shader button on the Light
Shader rollout before you see any changes take
effect.)
Interfa ce
Enable—When on, rendering uses the light shaders
you have assigned to this light. When off, the
shaders h ave no effect on rendering. Default=off.
Light S hader—Click the button to display a
Material/Map Browser (page 2–1256) and select a
light shader. Once you have selected a shader, its
name appears on the button.