Utilizing Lumen for Dynamic Global Illumination

You will implement Lumen to achieve high-quality, fully dynamic indirect lighting that responds instantly to changes in scene geometry and light sources.

In this lesson, you will learn how to configure and utilize Lumen to achieve real-time, high-fidelity global illumination that reacts instantly to your scene’s lighting and geometry.

Global Illumination (GI) is the process of simulating how light bounces off surfaces to illuminate areas not directly hit by a light source. Traditionally, this required "baking" lightmaps, which are static and inflexible. Lumen changes this by calculating these light bounces dynamically, allowing your scene to feel alive.

Configuring Lumen

To get started, ensure your project is set to Lumen under Project Settings > Rendering > Global Illumination. For the highest quality, you should also set your Reflections method to Lumen.

Scene Requirements

Lumen relies on two main components to track how light interacts with your world:

Mesh Distance Fields: Lumen uses these to understand the shape and volume of your objects. Ensure Generate Mesh Distance Fields is enabled in your Project Settings.
Surface Cache: Lumen creates a simplified representation of your scene's surfaces. When you move a light or an object, Lumen updates this cache to re-calculate the bounce lighting.

Dynamic Interaction

Because Lumen is fully dynamic, moving a Directional Light or changing a material's Emissive Color will cause the indirect lighting in your scene to update without needing to re-bake lightmaps.

If you have an object that emits light, simply set its material to use a constant:

// Within your Material Graph, use an Emissive node:
// Base Color: [Texture]
// Emissive Color: [Color * Intensity]

Ensure that "Use Emissive for Static Lighting" is disabled if you want the light to be dynamic; Lumen will automatically pick up the light contribution from emissive surfaces as long as the object is marked as "Visible" and "Cast Shadows."

If you find the lighting is not updating on small objects, check the object's Lumen Scene Lighting Quality or ensure the geometry is simple enough for the Mesh Distance Field to accurately represent it.

Key Takeaway: Lumen replaces static baked lighting by leveraging hardware-accelerated ray tracing or software-based distance fields to calculate light bounces in real-time, enabling instant visual feedback for dynamic environments.