--- title: "Introduction to Light Path Expressions" canonical: "https://documentation.chaos.com/space/VC4D/116850696/Introduction%20to%20Light%20Path%20Expressions" format: markdown --- ## **Overview** --- If you are not familiar with using Light Path Expressions (LPEs), this page is a good place to start. The sections below explain what LPEs are, how they work, and what are the possible use cases. > Macro (ui-text-box) > > The [Advanced Light Path Expressions article](https://docs-chaos.atlassian.net/wiki/spaces/VC4D/pages/116850700) goes into greater detail about complex LPE usage and concepts. ## **What are LPEs?** --- Light Path Expressions are a special type of render element with advanced capabilities. They use regular expression patterns to record selected events of light contribution along the path of a ray. This can be used for very fine control in compositing by allowing you to tweak, for example, the GI coming from lights, the environment or self-illuminating objects separately, each separate GI bounce, or the self-reflections of an object or the way SSS is seen behind refraction without re-rendering. The possible applications are practically endless. ## **Light Paths** --- ## **Ray Spawn Events and Scattering Types** --- ![image](media://396bc99e-cec3-46b7-87de-9ceb0da8c58b) A single volumetric event.  CVL ![image](media://6e995e0a-6c21-4ae7-a2cd-7574a4be9cb4) Multiple events: Glossy and specular refraction followed by diffuse reflection.  CL