V-Ray Bump Normals is a render element that stores the camera view as a normal map. The normals are generated using screen space which uses the XYZ orientation of the camera view. With Screen space, the X axis runs left-right across the view, Y runs up-down, and Z points out of the screen. Bump maps are also represented in this render element.
The Bump Normal Render Element is useful for adjusting lighting that comes from a particular direction. For example, faces of objects pointing toward the camera will be predominantly blue in V-Ray Bump Normals, so the lighting on such objects can be adjusted by using the blue channel in compositing software.