If disabled, the Luxology render results in a ray traced image.

By default, when Indirect Illumination is enabled, the Irradiance Caching method for radiosity also is enabled. This means that the Indirect Rays option is disabled in favor of the Irradiance Rays within the Irradiance Caching settings area.

Technically, Indirect Rays are the same as Irradiance Rays; however, both settings are available since the two forms of indirect illumination require vastly different numbers of samples.

Using fewer bounces lessens quality but increases performance. By increasing the number of indirect bounces, the Indirect Rays are fired from the initial surface and bounce off the first surface they hit then continue traveling and hitting surfaces until the maximum number of bounces is met.

As you add bounces, the number of calculations increase, as does render times. While the result is more accurate, there are naturally occurring diminishing returns in each additional bounce. Adjust your scene with a single bounce and then add additional bounces to see how they impact the end result.

For most exterior scenes a single bounce suffices. Interior scenes benefit from additional bounces, but you should rarely need more than 4 or 5.

If a scene is mostly illuminated by a single small area of light, adding bounces improves the overall brightness and look of the rendered image.

This is a useful way to optimize render times. Generally, reducing the indirect range improves render speed. However, setting this value too low creates unnatural lighting effects. In these cases, many rays that otherwise would have ultimately hit a geometric surface, resulting in a shadow, may get cut off early. They may illuminate the surface unrealistically, with the backdrop color, rather than shading it with the surrounding geometry. Leaving the value at 0 is similar to setting an infinite value. In other words, rays will not be terminated prior to striking the environment.

Another advantage in limiting the range of indirect rays is that, in large complex scenes, a limited Indirect Range allows geometry segments that are off-screen or in already completed buckets, to be flushed from memory more easily. This is because Indirect Rays may be stopped by the limited range before reaching the bounding boxes of those segments. Without being limited, such rays can cause all the polygons in those segments to be brought back into memory.

• None — No indirect caustics are rendered.
• Reflection — Only reflected indirect caustics are rendered.
• Refraction — Only refracted indirect caustics are rendered.
• Both — Both reflected and refracted indirect caustics are rendered.

Irradiance caching is used for computing global illumination on diffuse surfaces. It addresses the computation of indirect illumination bouncing off one diffuse object onto another. Irradiance caching is used to make this computation fast. The main idea is to perform the indirect illumination sampling only at a selected set of locations in the scene, store the results in a cache, and reuse the cached value at other points through fast interpolation.

Irradiance Caching relies on much higher quality samples distributed sparsely across the project whereas Indirect Illumination without Irradiance Caching uses lower quality samples at every pixel. Having two values allows you to easily switch between Irradiance Caching and traditional Indirect Illumination without constantly adjusting the number of rays for each sample.

After all rays have been fired for a particular irradiance evaluation, Supersampling looks at the resulting ray color of each hemisphere cell. It then sends additional rays through the cells that are very different from their neighbors, getting a more detailed look at high contrast areas of the environment, resulting in a more accurate estimate.

Currently about 25% more rays are fired, so for a setting of 100 rays, you get 125. The results, however, are better than if you used a setting of 125 without Supersampling because the rays for Supersampling are going in the more important directions. Leave on this option at all times; it improves your render quality with minimal performance impact.

Example showing subsurface scattering of light as it penetrates a material

With Direct Only enabled, rendered images still can contain effects from both indirect illumination as well as Subsurface Scattering, but the two will not affect each other. This is the default behavior for speed reasons.

When either or both of the indirect illumination settings are enabled, indirect illumination rays will be considered when evaluating Subsurface Scattering effects, with a resulting increase in the rendering time.

• Direct Only — Direct lighting only is considered.
• Indirect Affects Scattering — Indirect lighting is considered when calculating subsurface scattering.
• Scattering Affects Indirect — Subsurface scattering is considered when calculating indirect lighting.
• Both — Both the indirect lighting and the effect of subsurface scattering on indirect lighting, are considered in the rendering.

• First And Second Bounces - Both the first and second bounces will use Irradiance Caching and subsequent bounces will use Monte Carlo method.
• First Bounce Only - Only the first outward bounce from the camera will use Irradiance Caching, any subsequent bounces will use Monte Carlo method.
• Second Bounce Only- The first outward bounce from the camera will use Monte Carlo method and the second bounce will use the Irradiance Caching; and then any subsequent bounce will use Monte Carlo method .

Technically, Irradiance Rays are the same as Indirect Rays; however, both settings are available since the two forms of indirect illumination require vastly different numbers of samples.

For example, take a case where this value is set to three. If the point being shaded can find only two nearby previously computed values in the cache, then it forces the computation of a new value at the current point. The final irradiance at that point is a blend of all three values. In this way it tends to smooth out the shading. Generally, increasing this value improves render quality at the expense of render time.

The photon count is divided amongst all active 3D lights with a bias based on the power of the light.

Direct Caustics disabled (left) and enabled (right)