Well, 'light vs shadow light novel' could center around the concept of duality. The light might symbolize good, hope, or positive forces, while the shadow could stand for evil, mystery, or negative aspects. It may tell a story of a hero from the side of light facing challenges from the shadowy elements in the story's universe, with lots of plot twists and character development.
Since I haven't read the novel, I can't say for sure who the main characters are. They could be a hero who embodies light and a villain who represents shadow.
86 is indeed a light novel. It gained popularity as such and then branched out into manga. The light novel typically offers more detailed character development and in-depth exploration of the story's themes compared to the manga adaptation.
I'm not sure as I haven't read the specific 'light vs shade novel'. But typically, there would be a protagonist who is likely to be caught between the forces of light and shade.
Radiant is primarily a manga. It features detailed illustrations and a captivating plot that has attracted a wide audience. The manga version has a dedicated fan base.