8

1188 Chapter 15: Lights and Cameras
in the scene at once. If you need to adjust a specific
light, you can u s e the multiplier controls for energy
and photons. In general, you should rarely if ever
need to turn off Use Global Settings and specify
local light settings for indirect illumination.
Impor tant: In addition to the values specified here,
the light must also be set to generate caustics, global
illumination, or both. These controls are on the
mental
ray panel (page 1–121)
of the Obj ect Properties dialog.
You also need to turn on Caustics, Global, or both, on
the Render Scene dialog’s
Indirect Illumination rollout
(page 2–1187)
.
Inter face
Automat ically Calcula te E nergy a nd P hotons—When
on, the light uses the global light settings for
indirect illumination, rather than local settings.
Default=on.
When this toggle is on, o nly the controls in the
Global Multipliers group are available.
Global Multipliers group
Energy—Multiplies the global Energy value to
increase or decrease the energy of this particular
light. Default=1.0.
Caustic Photons—Multiplies the global Caustic
Photons value to increase or decrease the count of
photonsusedtogeneratecausticsbythisparticular
light. Default=1.0.
GI Photons —Multiplies the global GI Photons value
to increase or decrease the count of photons used
to generate global illumination by this particular
light. Default=1.0.
Manual Settings group
When Automatically Calculate is off, the Global
Multipliersgroupbecomesunavailable,andthe
manual settings for indirect illumination become
available.
On—When on, the light can generate indirect
illumination effects. Default=off.
Filter color—Click to display a Color S elector (page
1–157)
and choose a color that f ilters the light
energy. Default=white.
Energy—Sets the energy of the light. E nergy, or
"flux," is the amount of light used in indirect
illumination. Eachphotoncarriesafractionof
the light’s energy. This value is independent of
the light intensity determined by the li ght’s color
and Multiplier, so you c an use the Energy value
to fine-tune indirect il lumination effects without
changing the light’s other effects in a scene (such as
providing diffuse illumination). Default=1000.0.
Decay—Specifies how photon energy decays as
it moves away from the light source. Can equal
None, Inverse, or Inverse Square. Default=None.