In addition to setting ambient light with a dark gray color, we have set up two lights, a directional light and a spot light. The directional light is designed to illuminate only the sphere, both its outside and inside. Thus, we set two-sided lighting as true with the call to glLightModeli and enable the directional light (GL_LIGHT1) before constructing the geometry with a call to displaySphere. Last, we disable the directional light after displaying the sphere.