--- title: "Introduction to Light Path Expressions" canonical: "https://documentation.chaos.com/space/VRAYNUKE/110626236/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 will try to 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/VRAYNUKE/pages/110626238) 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, or 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://f2c15b3f-149b-4b6d-a7c6-1a908b28bb4e) A single volumetric event.  CVL ![image](media://90561d2f-7956-4c0e-aa3d-412bb72d226f) Multiple events: Glossy and specular refraction followed by diffuse reflection.  CL