The mental Indirect Illumination rollout provides controls for light behavior with the mental ray renderer. The settings on this rollout have no effect on rendering with the default scanline renderer, or on advanced lighting (the light tracer or a radiosity solution). These settings control how the light behaves when it generates indirect illumination; that is, caustics and global illumination.
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Modify panel > mental ray Indirect Illumination rollout
Indirect Illumination panel Caustics & Photon Mapping (GI) rollout. It is more convenient to adjust all lights in the scene at once. If you need to adjust a specific light, you can use 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. Indirect Illumination panel Caustics & Photon Mapping (GI) rollout. Interface
- Automatically Calculate Energy and Photons
- When on, the light uses the global light settings for indirect illumination, rather than local settings. Default=on.
When this toggle is on, only 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 photons used to generate caustics by this particular 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 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 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.
- 2.0 (inverse square) The energy decays at an inverse square rate. That is, a photon's energy is the inverse of the square of the distance (r) from the light source (1/r2).
In the real world, light decays at the inverse square rate, but this gives strictly realistic results only if you provide a realistic value for the energy of the light. You can use other values to help adjust indirect illumination without worrying about physical 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 used for caustics. Increasing this value increases the accuracy of caustics, 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 previewing caustic effects. Default=10000.
- GI Photons
- 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 illumination. 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 previewing global-illumination effects. Default=10000.