Even when the illumination equation is applied at each point of the faceted nature of the polygonal nature is still apparent. To overcome this limitation normals are introduced at each vertex.

• Usually different than the polygon normal
• Used only for shading (not backface culling or other geometric computations)
• Better approximates the "real" surface
  • Assumes the polygons were a piecewise approximation of the real surface (C⁰)
  • Normals provide information about the tangent plane at each point (C¹)