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Lighting & Shadows

Workingguide~2 min read

Light counts and shadow choices are among the biggest scene-level performance levers in UE5 - and among the easiest to audit.

On this page Light Mobility Shadow-Casting Lights Lumen Virtual Shadow Maps Scene Hygiene

5.1Light Mobility Sets The Price

Static, Stationary and Movable lighting compared as baked, mixed and dynamic setups, subject to renderer and project settings.
fig 12 - light mobility depends on renderer and project settings

Static lights bake to lightmaps (nearly free at runtime); Stationary lights bake indirect but compute direct lighting and shadows live (limit ~4 overlapping); Movable lights compute everything every frame. The audit rule mirrors meshes: nothing should be Movable that doesn't need to be.

5.2Shadowed Movable Lights - Check Shadow-Casting Lights

A movable point light casting shadows re-renders its surroundings into a shadow map - a point light does it in six directions. From the master checklist: keep light counts low, especially shadowed movable lights - one of the biggest scene-level wins. The audit passes:

  • Turn Cast Shadows off on fill/accent lights - most small lights read fine unshadowed.
  • Tighten attenuation radius - a light's cost scales with what it touches; use the Light Complexity view to see overlap. More than ~4 lights overlapping the same area is a red flag.
  • Set Max Draw Distance on small lights so they cull.
  • Reduce per-light shadow resolution where the fidelity isn't visible.

5.3Lumen: Measure The Cost Of Dynamic GI

Lumen delivers dynamic global illumination and reflections for a per-frame GPU cost driven by quality settings, screen percentage, and scene complexity (check stat gpu -> Lumen passes). The high-level levers: Global Illumination and Reflection quality scalability groups, Software vs Hardware Ray Tracing choice, and Surface Cache health - materials must be Surface-Cache-friendly (visualise with Lumen view modes). On tight budgets, baked lighting may suit static scenes; compare runtime cost, memory, and the workflow your project needs.

5.4Virtual Shadow Maps

VSM (the UE5 default) delivers crisp shadows but its cost scales with light count, resolution, and - critically - invalidations: anything moving (or animating via WPO) forces shadow pages to re-render. Keep WPO off distant things, keep movable objects minimal, and watch the VSM stats when shadows dominate stat gpu.

5.5Scene Hygiene

Volumetric fog on every light adds up - enable per-light volumetric contribution deliberately. Light functions are per-pixel material evaluations. IES profiles are cheap; light channels are organisational, not free. And the sun: one directional light, cascades tuned to gameplay distances, not defaults.

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