This is the documentation for Enlighten.
Light from the sky
When your level contains a Sky Light actor which is Stationary or Movable, Enlighten provides both direct and indirect sky lighting.
When using Enlighten, Distance Field AO is disabled for a Movable Sky Light. This combination is not currently supported.
Separate sky bounced lighting
By default Enlighten combines direct and indirect sky lighting which can look flat in outdoor areas when lit by sky lighting from above along with sun bounce from below. To prevent this, Enlighten provides the option to use separate sky bounced lighting for a small additional runtime cost.
In order to enable separate sky bounce, set r.Enlighten.SeparateSky=1 in DefaultEngine.ini.
The images below show combined sky and bounce on the left, and separate sky and bounce on the right.
