---
title: "Light Cache Settings"
canonical: "https://documentation.chaos.com/space/VRHINO/116132100/Light%20Cache%20Settings"
format: markdown
---
This page provides information about the Light Cache GI Engine in V-Ray for Rhino.

 

## **Overview**

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Light caching (called "light mapping" in older versions of V-Ray) is a technique for approximating the global illumination in a scene. This method was developed originally by Chaos Group specifically for the V-Ray renderer.

This rollout is available only if Light Cache has been chosen as either the **Primary Rays** or** Secondary Rays** GI engine in the [Global Illumination](https://docs-chaos.atlassian.net/wiki/spaces/VRHINO/pages/116130551).

 

 

## **UI Path**

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||V-Ray Asset Editor||** **>**  Settings **>** Global Illumination **>** Light Cache** 

(When Light Cache is set as the Primary or Secondary Rays engine.)

 

 

## **Parameters**

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### **Example: Subdivs **

 

The** Subdivs** parameter controls the number of rays that are shot into the scene and the "noise" quality of the light cache samples.

Here is a scene rendered with different settings for the **Subdivs** parameter (all other settings are the same). As more samples are added, the noise is reduced, but the render times increase. When the **Subdivs** parameter is increased twice, the light cache takes approximately 4 times as long to calculate.


 

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### **Example: Sample Size**

 

The **Sample size** parameter controls the size of the individual light cache samples. Smaller values produce a more detailed lighting solution, but are noisier and take more RAM. Larger values produce less detail but require less RAM and may be faster to compute.

Here is a scene rendered with different values for the** Sample size** parameter. All other values are the same. Note the light leak from the wall on the right in the last image - this is because samples from the other side of the wall are quite large (because of the Screen Scale) and end up being used on the side facing the camera (compare this with the World **Scale** in the above example). Note the difference in the noise level between the samples as well.


 

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### **Example: Retrace**

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The first set of images shows how the** Retrace **parameter can be used to reduce light leaks due to the light cache interpolation. The scene is an interior scene with parts of the exterior visible. The bright light cache samples from the exterior blend with the darker samples from the interior causing light leaks when the irradiance map is calculated. The** Retrace **option (with the default value of 1.0) successfully resolves the problem at the expense of slightly increased calculation time for the irradiance map. Without retracing, light cache samples from the bright exterior are mixed with the dark samples in the exterior causing light leaks. With light cache retracing enabled, the light leaks are successfully eliminated at the expense of slightly longer irradiance map calculation time.

 



## **Disk Caching**

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## **Notes**

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- Do not apply perfectly white or near-white materials to the majority of the objects in the scene, as this will cause excessive render times. This is because the amount of reflected light in the scene will decrease very gradually and the light cache will have to trace longer paths. Also avoid materials that have one of their RGB components set to maximum (255) or above.
- The Light Cache calculation cannot be distributed among several machines for distributed rendering.
- When using Auto Exposure/Auto White Balance options of the camera, make sure to select Light Cache as a secondary GI engine. Light Cache Disk Caching mode is not supported, use the Single Frame mode instead.