Light Source and Shadow
Light source is primarily for the benefit of the background painter. To assist in the creation of lighting and shadows, the layout artist will add Light Source Arrows to the background. The 3D ARROW with a line through it, and the letters L/S can be placed anywhere on the layout, provided, the direction of the arrow reflects the direction of the light. Below are four of many possible angles for the light to travel.

Light and shadow are based on perspective methods. In this section I wanted to mention the 3D Arrows and their use. For further reading of light and shadow check out any art book or web page on the topic. Here are a few treatments of light source in a tonal stage of the process.

This is a great example of a very strong light source. Without accurate direction from the layout artist, the background painter would guess from the storyboard where shadow and light fall. I have supplied my thumbnail tonal with the finished blue tonal for comparison of detail, blocking in of shapes, and use of shade line.

Form and Blocking
Form and Blocking, as explained earlier, are not that different from Form and Mass. The reason why I split this section up, was to first define one, two and three point perspective, and now, to define blocking in of shapes and form.

I think animation colleges and universities need to direct attention to blocking in shapes and forms in layout or even animation. By understanding how to block in layout elements so they physically read well and frame the action, this will also increase the silhouette strength of the animation characters. If by blocking in an object it becomes unrecognizable, adjust it so it is readable. Add texture to the most prominent item. Add halftone values to tie the areas of light and dark together. Walt Stanchfield has demonstrated this knowledge in many official and unofficial releases of his work. I suggest researching his name for further details.

How we define that form in our composition also defines the emotional response we will get from the audience.