Evaluating Scene Requirements for Dynamic Lighting

In this lesson, you will learn how to strategically evaluate your scene’s geometry and gameplay needs to decide when Lumen’s dynamic global illumination is the superior choice over traditional baked lighting.

The Trade-off: Flexibility vs. Overhead

Choosing between baked lighting (Lightmass) and Lumen isn't just about graphics; it’s a decision about your project’s architectural constraints. Baked lighting is incredibly performant because it stores light data in textures, but it is "static"—any changes to light intensity, color, or object placement during gameplay will not be reflected.

Lumen, by contrast, provides real-time bounce lighting and dynamic shadows, making it the industry standard for modern, high-fidelity experiences. However, it is computationally expensive. Before committing to Lumen, you must analyze three core criteria:

1. Dynamic Content: Does your game feature time-of-day systems, destructible environments, or moving light sources? If the answer is yes, baked lighting will fail to meet your visual requirements, and Lumen becomes the necessary engine.
2. Environment Complexity: Since Lumen relies on Surface Cache and signed distance fields (SDFs), scenes with highly dense, thin, or non-manifold geometry can cause lighting artifacts. If your scene is dominated by complex, thin geometry that doesn't play well with mesh distance fields, you might find that baked lightmaps offer higher stability.
3. Target Platform Budget: Even with hardware-accelerated ray tracing, Lumen consumes significant GPU resources. Check your r.Lumen.DiffuseIndirect.Allow and r.Lumen.Reflections.Allow budgets. If your scene requires high-end performance on consoles or mobile, evaluate if your GPU overhead allows for these passes.

Implementation Logic

You can evaluate your lighting needs at runtime or during development using console variables to toggle features. To compare, you might use a simple approach to disable Lumen features in specific low-performance zones:

// Example of checking global illumination status before spawning heavy dynamic actors
if (GetWorld()->GetSubsystem<ULumenSceneSubsystem>()->IsLumenEnabled()) {
    // Proceed with complex dynamic lighting interactions
} else {
    // Fallback to simpler, static-friendly lighting strategies
}

By balancing your need for real-time reactivity against your scene's complexity and hardware target, you ensure your lighting solution supports your game design rather than hindering it.

Key Takeaway: Prioritize Lumen when your design requires dynamic environmental changes, but revert to baked lighting if your geometry constraints or hardware performance targets cannot sustain the GPU cost of real-time global illumination.