Best way to apply light on LOD based terrain

I’m trying to render light on a LOD-based terrain with shaders but whenever terrain level detail gets lowered it looks very bad (Probably cause of drawing larger triangle that has only one normal), i couldn’t come up with solution. I tried both storing normals into VBO and rendering with normal texture neither gave good result

I’m using simple LOD algorithm that divides map into blocks and calculates level of detail.

I’ll make it simpler (Probably)

What is best way to render light by texture normal for its original texture which is detail of a terrain that uses LOD.
Low level of detail will show larger triangles with single set of normals which looks very rough :confused: