Spectral Fog Volume
Spectral Fog VolumeA Spectral Fog Volume defines a box of local volumetric fog. Add it from Place Actors > Spectral and fit its bounds using the face handles.
Fog volume properties update the rendered fog without a lighting bake. If it uses baked probe illumination, changes to that lighting source still require a bake.
Spectral Fog Volume is the bounded, local option. Probe fog lighting also supports Unreal's Exponential Height Fog with Volumetric Fog enabled. You can use native height fog without placing a Spectral fog box; its non-volumetric fog approximation is separate from the probe-lighting integration.
Bounds and overlaps
Smaller overlapping fog boxes take priority. There is no separate numeric Priority control on this actor. A smaller box with Density: 0 can define a clear region within a larger fog region.
Scale To World
Fits selected fog volumes around registered, visible, static, shadow-casting scene geometry, excluding scalable volume actors and sky geometry. It resets rotation and scale, centers the box on the collected bounds, and adds Fade Distance as padding.
Check the result afterward. Extending fog coverage does not automatically extend the probe volumes that light it.
probe volumesFog
Enabled
Default: enabled.
Toggles this volume's contribution without deleting it. This is separate from Use Probe Fog Lighting, which changes the lighting source used by fog.
Density
Default: 0.1 per meter. Minimum: 0; slider up to 1, without a declared hard maximum.
Controls how strongly fog affects light traveling through it. Higher values make it thicker; lower values make it clearer. A longer path through the same density produces more accumulated fog.
At 0 the region is clear. In a smaller overlapping volume, this can cut a clear region into a larger fog volume.
Color
Default: white. RGB control.
Scattering color of the fog. It tints the light scattered toward the view. It is not the editor Fill Color and does not set the volume boundary's appearance.
Emissive
Default: black. RGB control.
Adds the fog's own emitted contribution, multiplied by density. Black adds none. It does not require that the scene contain an emissive surface.
This differs from Fog Emissive in the Features tab, which scales a baked lighting channel from emissive surfaces.
Fade Distance
Default: 100 cm. Minimum: 0.
Softens density inward from the box boundary. Larger values create a wider internal transition; smaller values make a sharper boundary.
This fade consumes space inside the box. A very large fade relative to the box size can leave little fully dense interior.
Fog Fade Height
Default: 0. Range: 0 to 1.
Fraction of the box height used to fade toward its local top. 0 disables this height fade; 1 spreads it across the whole height.
The height direction follows the box's local orientation. This is separate from the boundary Fade Distance.
Fade Height Falloff
Default: 1. Minimum: 0.01; slider range: 0.1 to 8. Available when Fog Fade Height is above 0.
Shapes the height fade. Higher values concentrate more of the fog toward the bottom. Lower values retain more density toward the top.
It changes the curve, not the bounds or total fade-height fraction.
Scattering Distribution
Default: 0.2. Range: -0.9 to 0.9.
Controls the direction in which fog scatters incoming light. 0 is even scattering, positive values favor forward scattering, and negative values favor backward scattering.
This can change the apparent brightness strongly as the view turns relative to the light. It is not simply a density multiplier. Fog Probe Directionality is a different control for the directional lighting sampled from probes.
Static Lighting Scattering Intensity
Default: 1. Minimum: 0; slider up to 10, without a declared hard maximum.
Scales the static-lighting contribution scattered by this volume, from baked probes or Unreal's volumetric lightmap path. 0 removes that static-lighting contribution without setting the fog density to zero.
Use the volume value for a local balance. Use the Features tab's fog multipliers for the shared probe-lighting balance.
View distance
View Distance
Default: 10,000 cm (100 m). Minimum: 1 cm.
Maximum distance from the camera for this fog. The shared grid uses the farthest requirement among visible fog volumes.
Increasing it extends coverage but spreads a finite number of depth slices across more space. Consider Grid Size Z when distant coverage starts losing detail.
View Fade Distance
Default: 1,000 cm (10 m). Minimum: 0.
Distance over which fog fades before its far cutoff. Larger values make the transition less abrupt. It does not extend View Distance.
Start Distance
Default: 0 cm. Minimum: 0.
Distance from the camera before fog begins. Increase it to keep the immediate camera region clearer. It is not an offset to the actor's box.
Near Fade In Distance
Default: 100 cm. Minimum: 0.
Length of the fade after Start Distance. A longer fade makes the near-camera transition softer; 0 removes that transition interval.
Editor visualization
Show Fill
Default property value: disabled.
Shows the editor's box fill, subject to placement defaults. The fill can be visible even when rendered fog is disabled or has zero density.
Fill Color
Default: translucent blue, alpha 0.05.
Sets editor fill color and opacity only. Use Color under Fog to change the rendered fog's scattering color.
Render Fill On Top
Default: enabled.
Draws the editing fill through geometry so the full region remains visible. Disable it for an unobstructed view of occluding surfaces.
Blueprint updates
Refresh Fog is a Blueprint-callable update for property changes made through scripts. Transform changes are tracked automatically. If a script changes fog properties, refresh the fog instead of assuming a lighting rebake is needed.
Bounds, density, scattering, and camera fades are per volume. The Features tab controls shared probe-lighting balance and project grid quality. Changing one volume does not create a separate high-resolution grid just for that actor.