Common problems and solutions

Long precompute times

For a typical level, the Enlighten precompute should only take a few minutes. Even for very large levels, a distributed precompute should never take more than an hour. If your precompute times are much longer:

• Make sure the level is configured well for Enlighten. To learn how to do this, see the beginner tutorials.
• If your level contains a single large Landscape actor, split the actor across multiple sub-levels and reduce the lighting resolution for the distant parts of the Landscape.
• If your level contains large unlit translucent meshes such as light shafts and water surfaces, exclude these meshes from the radiosity computation.
• If you've changed the System Voxel Size or Dependency Included System Distance in world properties, try reverting to the default value.

Precompute memory limit

When your computer doesn't have enough physical memory to complete a precompute task, the precompute stops and reports a "Reached the maximum heap size limit" error.

This can happen when your level is unusually large or complex, or the computer has unusually little physical memory installed. It can happen intermittently when running the distributed precompute if one of the agents involved has unusually little physical memory.

To fix this, make sure the computer has sufficient physical memory.

Light leaks through walls

This may be caused by geometry that spans a wall separating dark and light areas of your level, such as floors that span the inside and outside of a building and thus see light from the outside. To fix the leak, you can split the floor mesh where it meets the wall.

By default, the direct light from a Spot Light actor may leak through walls, even when Cast Dynamic Shadows is enabled. To prevent this, you can enable Cast Dynamic Enlighten Shadows, or make sure the cone doesn't cross the wall.

Dark or black spots

Dark or black patches or spots can appear in areas with visible invalid back-faces in the contributing geometry. To make the back-faces easier to see (highlighted in orange), use Show > Enlighten > Radiosity Back-faces.

To reduce these spots:

• Avoid using the lighting modes Contribute Lightmap and Contribute Probe with "open" meshes that use materials with Enlighten Backface Type set to Invalid. Make sure these meshes are closed, or use the Detail, Probe or Disabled lighting modes.
• Avoid using the lighting modes Contribute Lightmap and Contribute Probe with closed meshes that have infinitely thin parts. Make sure all parts of the mesh have non-zero thickness, or use the Detail, Probe or Disabled lighting modes.

Black or unusual splotchy lighting can also be a result of self-overlapping UVs in meshes. When authoring static meshes for your level, make sure the UV channel specified in the Light Map Coordinate Index contains no self-overlapping UVs.

Seams in indirect lighting

Enlighten can prevent seams in the indirect lighting only when meshes are closely aligned along the edge where they meet. To minimize seams, make sure the lightmap UVs for both meshes are aligned, not at angles or with a large size disparity.

Decals not lit by Enlighten

This is caused by a known UE4 limitation (UDN) which affects any lighting applied in the base pass, including Lightmass and Enlighten.