Information/Guides on Implementing a render pass/feature

I am game play dev looking to learn more on the Rendering side as I work on my solo project. I am at an impasse on how to properly handle this situation. I am working on a night time level and have the dark level nearly prefect for the feeling and model I am going for. However the player character model and NPC near are too dark that it hear to where you are going on attacking. Being a game play programmer, the first though is to have a 2nd direction light with no shadows and only effect the character layer. Seems wasteful to have an additional realtime light for this. Next thought was a custom render pass which increase the white levels on game object in the character layers based on distance from camera. I am more I looking to this the more I feel out side of my realm of known. Any good sources on this ?