Accessing "Detailed Lighting" Data in Code for Gameplay

You’re right, I missed the render target part. Sorry about that :-/

I think you might be able to do it as part of the render target post process. This link has a couple of potentials

https://www.reddit.com/r/unrealengine/comments/1eys6af/how_do_i_access_or_replicate_the_lighting_only/