Quick answer: Hardware ray tracing needs DirectX 12 (or Vulkan), a DXR-capable GPU, the Support Hardware Ray Tracing project setting with the editor restarted, and the compute skin cache for skeletal meshes. Lumen additionally needs Use Hardware Ray Tracing when available. If it is on but meshes are missing from reflections, check Visible in Ray Tracing and Nanite fallback meshes.
You tick the box, restart, and reflections still look like software Lumen, or the option is greyed out. Hardware ray tracing in Unreal has several requirements that all have to line up, and the editor does not always tell you which one is missing.
Requirements checklist
- GPU: one with DXR support, such as NVIDIA RTX 20-series or newer, AMD Radeon RX 6000-series or newer, or Intel Arc. GTX cards and most integrated GPUs fall back to software.
- Driver and Windows: a current GPU driver and an up-to-date Windows 10 or 11.
- RHI: Default RHI set to DirectX 12 under Project Settings > Platforms > Windows. Ray tracing does not exist on DirectX 11. Recent UE5 versions also expect the SM6 shader format to be targeted.
- Project setting: Project Settings > Engine > Rendering > Hardware Ray Tracing > Support Hardware Ray Tracing, followed by an editor restart. Shaders recompile, which takes a while the first time.
- Skin cache: Support Compute Skin Cache (Rendering > Optimizations) must be on for skeletal meshes to appear in ray tracing; the editor prompts for this.
Confirm the RHI actually enabled it
Check the Output Log after startup. The D3D12 RHI logs the ray tracing tier it found, and if ray tracing is unavailable it says so. If you see LogD3D11RHI lines, the editor is running on DirectX 11, which is the most common reason for a greyed-out or ignored setting: the Default RHI is DX11, or the editor was launched with -dx11.
With ray tracing active, Show > Visualize gains ray tracing debug views. If those views are missing, ray tracing is not running.
Make Lumen use it
Enabling ray tracing does not by itself switch Lumen to hardware tracing. Also enable Use Hardware Ray Tracing when available in the Lumen section of Rendering settings. In the Post Process Volume, Lumen's Ray Lighting Mode controls whether reflections use the surface cache or full hit lighting; hit lighting gives sharper, more accurate reflections at a higher cost.
[/Script/Engine.RendererSettings]
r.RayTracing=True
r.SkinCache.CompileShaders=True
r.Lumen.HardwareRayTracing=TrueRay tracing is on but objects are missing or wrong
- Visible in Ray Tracing is a per-component flag. If it was turned off for performance, the object is invisible to rays: missing from reflections and casting no ray-traced shadow.
- Nanite meshes are ray traced against their fallback mesh, not the full-detail geometry. A very coarse fallback shows up as low-poly shapes in reflections; lower the fallback's relative error on the mesh to improve it.
- World Position Offset (wind on foliage, for example) is not evaluated for every object in the ray tracing scene by default, so animated foliage can shadow and reflect in its rest pose.
- Skeletal meshes without the skin cache are skipped, see the requirements above.
In the packaged game
A packaged game that starts on DirectX 11, through a fallback or a -dx11 launch option, has no hardware ray tracing even on an RTX card. Design so the game still looks acceptable with software Lumen, and treat hardware ray tracing as an enhancement. Players without a DXR GPU are a large share of the PC audience.
Ray tracing crashes are driver-specific
Ray tracing paths are newer and more driver-sensitive than raster paths, and their crashes cluster by GPU vendor and driver version. Bugnet's Unreal SDK files fatal errors with the GPU and OS attached and groups identical failures, so you can tell “crashes on one driver branch” from “crashes everywhere” on the first day.
Related problems
- Fix: Unreal Lumen Not Working in a Packaged Build
- Fix: Unreal Lumen Reflection Noise on Rough Surface
- How to Fix “DX12 is not supported on your system” in Unreal Engine Games
Frequently asked questions
Why can’t I enable hardware ray tracing in Unreal Engine 5?
The editor is probably running on DirectX 11, the GPU has no DXR support, or the editor was not restarted after enabling Support Hardware Ray Tracing. Set the Default RHI to DirectX 12 and restart.
Does enabling ray tracing make Lumen use it automatically?
No. Also enable Use Hardware Ray Tracing when available in the Lumen settings.
Why are some objects missing from ray-traced reflections?
They may have Visible in Ray Tracing turned off, be skeletal meshes without the compute skin cache, or be Nanite meshes whose fallback mesh is too coarse.
Hardware ray tracing is a layer on top. Make sure the game still looks right without it.