2009

Manual Settings group
When Automatically Calculate is off, the Global Multipliers group becomes
unavailable, and the 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 Selector on page 391 and choose a color
that filters the light energy. Default=white.
Energy Sets the energy of the light. Energy, or "flux," is the amount of light
used in indirect illumination. Each photon carries a fraction of the light’s
energy. This value is independent of the light intensity determined by the
light’s color and Multiplier, so you can use the Energy value to fine-tune
indirect illumination effects without changing the light’s other effects in a
scene (such as providing diffuse illumination). Default=50000.0.
Decay Specifies how photon energy decays as it moves away from the light
source. Range=0.0 to 100.0. Default=2.0 (inverse square; physically correct
falloff).
This value is applied as an exponent to the distance (r) between the light
source and each indirectly illuminated point to determine the energy at that
point, in the formula 1/r[Decay]), and is intended for tweaking the GI solution.
The most commonly used values are:
■ 0.0 (no decay) The energy doesn't decay, and photons provide equal
indirect illumination throughout the scene.
■ 1.0 (inverse) The energy decays proportionally to its distance from the
light, with linear falloff. That is, a photon's energy is 1/r, where r is the
distance from the light source.
5114 | Chapter 18 Lights and Cameras