Lumen not turning on in 5.5-5.8, but works fine in 5.0

Development Architectural and Design Visualization
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1

hello everyone! I have issue turn on Lumen, for some reason its worked pefectly in 5.0, I turned it on according tutorials, but in 5.6-5.8 version its not working, when I switch from Lit to Lumen its said its disabled. Same in 5.5 however switch from Lit to Lumen doesnt displays error

GI and reflections set to Lumen
Infinite extent set to on

2

the two usual reasons Lumen shows as disabled in newer versions on a project that “worked in 5.0”:

  1. the project is using the Mobile or Desktop-forward rendering path. Lumen requires Deferred Renderer. Project Settings → Rendering → check Mobile/Priority shading path; in .ini terms r.Mobile.ShadingPathMode / forward shading settings. a 5.0 project built off the mobile-forward template behaves exactly like this: the GI dropdown is set to Lumen but the editor reports it cannot enable it. also check r.ForwardShading is off.
  2. hardware ray tracing is disabled and the fallback path is off too. Lumen in 5.5+ needs either DX12 with SM6 (Project Settings → Platforms → Windows → Default RHI: DirectX 12, and SM6 enabled) or software ray tracing via distance fields (r.Lumen.SoftwareRayTracing 1 requires Generate Mesh Distance Fields = on). if someone turned off Generate Mesh Distance Fields and the RHI is DX11, Lumen has no path at all and disables itself.
    quick console triage, in this order:
  • r.Lumen.HardwareRayTracing — does the console know the variable at all (if unknown, the feature never loaded, shading path problem)
    • r.DynamicGlobalIlluminationMethod — should be 1
    • r.SkinCache.CompileShaders and ray-tracing support if you want HW Lumen
    • check the message log after toggling — 5.5+ tells you WHY it disabled GI instead of failing silently
      also worth knowing: “Infinite extent” only affects the Lumen scene bounds, it is not the enable switch. and if the project was upgraded across 5.1 → 5.4+, verify DefaultEngine.ini still has r.DynamicGlobalIlluminationMethod=1 under [/Script/Engine.RendererSettings] and the section was not left in a duplicated older ini (duplicated sections in DefaultEngine.ini are a real thing after upgrades and the last value wins — check that there is exactly one).