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
the two usual reasons Lumen shows as disabled in newer versions on a project that “worked in 5.0”:
- 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.
- 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)
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- r.DynamicGlobalIlluminationMethod — should be 1
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- r.SkinCache.CompileShaders and ray-tracing support if you want HW Lumen
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- 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).
One more angle that caught me out on an upgraded project, in case the deferred / ray tracing checks above are already correct:
Isolate project vs. engine first. Create a brand-new blank project in 5.6 (not a copy of the 5.0 one) with the default settings, drop in a simple room with one Rect Light, and switch the view mode to Lumen. If Lumen works there, your install and GPU driver are fine and the problem is a setting that travelled with the old project — which is very common, because Project Settings are only half the story. Old Config/DefaultEngine.ini values can quietly override the UI.
Things to compare between the working new project and the broken one:
- Project Settings > Rendering: Default RHI is DirectX 12, and under Platform > Windows, D3D12 is using Shader Model 6. If it fell back to SM5, Lumen will report as disabled even though the GI dropdown says Lumen.
- Generate Mesh Distance Fields is enabled. Without it, software ray tracing has almost nothing to trace, and scenes can look like Lumen is simply off, especially indoors.
- Allow Static Lighting is off for a fully dynamic Lumen scene, and you have deleted / disabled any old baked-lighting setup that is still being referenced.
- There is no global Post Process Volume in the level setting Global Illumination Method back to None or Screen Space and overriding the project setting. I spent an embarrassing amount of time on exactly that — the project was right, one unbound volume was wrong.
- Engine Scalability is not on Low / Medium for Global Illumination while you are testing. Set scalability to Epic temporarily just to rule it out.
After changing RHI, distance fields or static lighting, do a full editor restart and let shaders finish recompiling before judging it — Lumen often still shows as disabled in the view mode during that first compile, and toggling Lit > Lumen too early makes it look like the change did nothing.
If the fresh project also fails, then I would look outside the project: update the GPU driver, and check Output Log on startup for lines mentioning Lumen, ray tracing or SM6 — 5.5+ usually logs a specific reason there rather than just refusing. Posting that log line, plus your GPU and whether the fresh-project test worked, would probably let someone here pinpoint it in one reply.
Edit to add: that checklist habit — isolate one variable, test it clean, and only then change the next thing — is one I picked up doing practical, hands-on troubleshooting work, fixing one small broken setting at a time rather than rebuilding everything, in much the same way as the folks at a small dev studio.