lighted color of a vertex is the sum of the material
        emission intensity, the product of the material ambient
        reflectance and the lighting model full-scene ambient
        intensity, and the contribution of each enabled light source.
        Each light source contributes the sum of three terms: ambient,
        diffuse, and specular. The ambient light source contribution is
        the product of the material ambient reflectance and the light's
        ambient intensity. The diffuse light sou