Final answer:
The planes that are closer to and facing the light source are lighter than the planes that are further from it and facing away.
Step-by-step explanation:
The planes that are closer to and facing the light source are lighter than the planes that are further from it and facing away. This is because the light source illuminates the closer planes more directly, resulting in a brighter appearance. On the other hand, the planes that are further away and facing away from the light source receive less direct illumination and appear darker.