rce contribution is the
        product of the material diffuse reflectance, the light's
        diffuse intensity, and the dot product of the vertex's normal
        with the normalized vector from the vertex to the light source.
        The specular light source contribution is the product of the
        material specular reflectance, the light's specular intensity,
        and the dot product of the normalized vertex-to-eye and
        vertex-to-light vectors, raised to the power of the shininess
       