Lumen

Lumen is an Unreal Engine Mechanic used in Fortnite: Battle Royale that allows for high-quality ray traced reflections on glossy materials and water and real-time global illumination.
Lumen is currently unavailable in Fortnite: Save the World and Fortnite: Creative. Lumen can only be enabled in Fortnite: Battle Royale on PC, Playstation 5 and Xbox Series X Currently.
== Functions ==
* Lumen uses Software Ray Tracing through Signed Distance Fields by default, but can achieve higher quality on supporting video cards when Hardware Ray Tracing is enabled.
* Lumen generates an automatic parameterization of the nearby scene's surface called Surface Cache. It is used to quickly look up lighting at ray hit points in the scene. Lumen captures the material properties for each mesh from multiple angles. These capture positions (called Cards) are generated offline for each mesh. 
* Lumen features trace rays against the screen first (called Screen Tracing or Screen Space Tracing), before using a more reliable method if no hit is found, or the ray passes behind a surface. Screen tracing supports any geometry type and is useful for covering up mismatches between the Lumen Scene and triangle scene. 
* Lumen provides two methods of ray tracing the scene: Software Ray Tracing and Hardware Ray Tracing. 
** Software Ray Tracing uses Mesh Distance Fields to operate on the widest range of hardware and platforms but is limited in the types of geometry, materials, and workflows it can effectively use. 
** Hardware Ray Tracing supports a larger range of geometry types for high quality by tracing against triangles and to evaluate lighting at the ray hit instead of the lower quality Surface Cache. It requires supported video cards and systems to operate. 
== Usage in Fortnite ==
With the launch of Chapter 4: Season 1, Lumen was introduced for Ray Tracing and Global Illumination exclusively in Fortnite: Battle Royale, bringing an entire visual redesign. This allowed for more lighting, reaction of characters model with the environment, bounce lighting and scattering of light.
Category:Gameplay
Category:Unreal Engine Features