This is the documentation for Enlighten.

Probe lighting

The UE4 renderer samples Enlighten probes to provide diffuse indirect lighting for both static and non-static actors.

It can be difficult to produce efficient lightmap UVs for meshes with complex organic shapes or many small parts; these meshes might be more efficiently lit using probes.

Enlighten probes provide lighting for a volume of space. Enlighten determines the nearby probes to sample from based on the location of each mesh.

Enlighten automatically places probes in your level. You only need to specify the desired probe spacing for each area of the level.

The image above shows probes automatically placed by Enlighten. Enlighten varies the density automatically, so there are fewer probes in the middle of the room.