Using Phong Shading
Phong shading is a process that simulates the effect of smoothly curved lighting across surfaces which are actually flat. It is done by modifying the surface's angle at each step across the surface to smoothly blend it into the surrounding surfaces.
ArghRad implements Phong shading on a per-surface basis. To use it, give the desired surface a light value, but do not set the light flag. This value acts like a "curve ID tag". When it lights that face, it will smooth together the lighting with any touching faces that share the same "ID tag" light value. Two touching surfaces can belong to two different curves simply by using different tag values.