User blog comment:Emillianna/What is Lumen Histoire?/@comment-77.242.116.97-20140429114701/@comment-24816171-20140429170451

It could be linked to Zeref - that would explain why Makarov's son thought it's dark. Somehow, he might heard Lumen Histoire is connected with Zeref and that made him think of it as dark. And Zeref surely has a light half :)