Bump maps use textures to perturb an object’s shading normals to create the illusion of relief on the object’s surface. Because they do not actually change the object’s geometry, they are best suited to creating fine detail that does not come too far off the surface.
Shaders Used for Bump Mapping
When Not to Use Bump Maps
Because bump maps do not actually alter object geometry, their limitations can become apparent when too much relief is required, as you can see on the sphere shown below.