System dependencies control whether or not light transfers between systems. By default, all system dependencies are automatically calculated during the CalculateSystemDependencies stage of the precompute. Setting up system dependencies can significantly reduce light transport time during the precompute.

If the loaded scene has more than one system, the System Dependencies tab becomes available. When you click on this tab, the "selected" system is shown in yellow and its dependencies are shown in green.

To select a system, use the context menu.

Revert dependencies	Revert to the dependencies initially loaded with the scene.
Save dependencies	Save dependencies to disk. These dependencies are used for the next precompute of the scene.
Include all	Set all dependencies of this system to Include.
Global include all	Set all dependencies of all systems to Include.
Auto all	Set all dependencies of this system to Auto.
Global auto all	Set all dependencies of all systems to Auto.
Exclude all	Set all dependencies of this system to Exclude.
Global exclude all	Set all dependencies of all systems to Exclude.
Calculate dependencies	Calculate dependencies using the precompute API.
Load calculated deps	Load the calculated dependencies information (to allow changing the visibility requirement).
Selected system	Use the slider to select a system.
Flash	Tick the box to make the currently selected system flash so it can be easily identified.

There are three available edit modes, controlled by the radio button.

Manual edit

Add or remove a dependency by right-clicking on the dependency and selecting from the context menu.

Radius cutoff

Enable the Radius cutoff controls:

The Radius cutoff slider allows you to set the radius cutoff for the selected system. All systems within this radius become dependencies of the selected system.
Click Apply radius to all systems to define dependencies for all systems based on the Radius cutoff.

Calculated

Enable the Calculate and Load calculated deps buttons, and show the Radius cutoff and Visibility cutoff sliders that control the inputs to the precompute API function.

The image below shows the effect of removing the interior arches' dependency on the background hills:

After the dependency is removed, no light is transported from the background hills to the interior arches. This process is not two way; the background system still receives light from the interior arches system. To remove the dependency on the interior arches, you must select the background system, then right-click on the interior arches system and select Remove dependency from the context menu.

Make sure to save the dependencies before precomputing the scene.