# [Lumen General Setting Optimizations](https://learn.arm.com/learning-paths/mobile-graphics-and-gaming/best-practices-for-hwrt-lumen-performance/8-lumen-general/)

## In this learning path

- [Introduction](https://learn.arm.com/learning-paths/mobile-graphics-and-gaming/best-practices-for-hwrt-lumen-performance/)
- [Lumen and Ray Tracing](https://learn.arm.com/learning-paths/mobile-graphics-and-gaming/best-practices-for-hwrt-lumen-performance/1-ray-tracing/)
- [Acceleration Structure](https://learn.arm.com/learning-paths/mobile-graphics-and-gaming/best-practices-for-hwrt-lumen-performance/2-acceleration-structure/)
- [Only Add Important Objects into Ray Tracing](https://learn.arm.com/learning-paths/mobile-graphics-and-gaming/best-practices-for-hwrt-lumen-performance/4-add-object/)
- [Take Full Advantage of Instancing](https://learn.arm.com/learning-paths/mobile-graphics-and-gaming/best-practices-for-hwrt-lumen-performance/5-instancing/)
- [Optimize Acceleration Structure](https://learn.arm.com/learning-paths/mobile-graphics-and-gaming/best-practices-for-hwrt-lumen-performance/6-optimize-as/)
- [Reduce Acceleration Structure Run-time Update Cost](https://learn.arm.com/learning-paths/mobile-graphics-and-gaming/best-practices-for-hwrt-lumen-performance/7-run-time-update/)
- [Lumen General Setting Optimizations](https://learn.arm.com/learning-paths/mobile-graphics-and-gaming/best-practices-for-hwrt-lumen-performance/8-lumen-general/)
- [Next Steps](https://learn.arm.com/learning-paths/mobile-graphics-and-gaming/best-practices-for-hwrt-lumen-performance/_next-steps/)

We now look at how best to optimize with the Global Illumination settings. To use Lumen in your game scene, you can add a **Post Process Volume** actor (found under Place Actors > Visual Effects). Within the details panel of **Post Process Volume**, there are several options that you can change and amend. During the development of the Lumen content, **“Steel Arms”**, we found a few recommended values for these options that are suitable for Android devices. The following images show all of the option values that were used in **“Steel Arms”** with some additional explanation provided.

## Global Illumination Settings

![Figure1. These global illumination parameters are used in our Lumen content - Steel Arms.](https://learn.arm.com/learning-paths/mobile-graphics-and-gaming/best-practices-for-hwrt-lumen-performance/images/gl-setting.png)  
Figure1. These global illumination parameters are used in our Lumen content - Steel Arms.

### Lumen Scene Detail
• Higher values ensure that smaller objects contribute to Lumen lighting but they do increase the GPU cost.

### Final Gather Quality
• This controls the density of the screen probes but note that higher values will increase the GPU cost.  
• **1.0** strikes a good balance between performance and quality for mobile games.

### Max Trace Distance
• This controls how far the ray tracing will go; keeping the number small decreases the GPU cost.  
• Do not set it to be larger than the size of the scene.  
• Smaller values can also reduce ray incoherence.

### Scene Capture Cache Resolution Scale
• This controls the surface cache resolution; smaller values save memory.

### Lumen Scene Lighting Update Speed
• This can be kept low if lighting changes are slow to save GPU cost.  
• **0.5 ~ 1.0** strikes a good balance between performance and quality for mobile games.

### Final Gather Lighting Update Speed
• This can be kept low if slow lighting propagation is acceptable.  
• **0.5 ~ 1.0** strikes a good balance between performance and quality for mobile games.

## Lumen Reflection Settings

![Figure 2. These reflection parameters are used in our Lumen content - Steel Arms.](https://learn.arm.com/learning-paths/mobile-graphics-and-gaming/best-practices-for-hwrt-lumen-performance/images/reflection-setting.png)  
Figure 2. These reflection parameters are used in our Lumen content - Steel Arms.

### Reflection Quality
• This controls the reflection tracing quality, essentially the resolution of the reflection.

### Ray Lighting Mode
• The default (and recommended for mobile games) mode is **Surface Cache**, which reuses surface cache data for reflection.  
• The **Hit Lighting** mode is available when using hardware ray tracing; it evaluates direct lighting instead of using the surface cache. It offers better quality but at a higher GPU cost and can also reflect the lighting of skinned meshes which **Surface Cache** mode cannot. **Hit Lighting** is not yet supported on mobile devices.

### Max Reflection Bounces
• This controls the number of reflection bounces; higher values increase the GPU cost.  
• **1** is recommended for mobile games.

This learning path has taken you through some key areas and best practices for using and optimizing hardware ray tracing with Lumen.