Aha.  I see.  Thanks for the explanation, Connie.

Um... what happens if there are trenches, with the light directly overhead, the bottom of the trenches may be lit like the tops of the trenches, (- if they are wide,) with only shadow at the edges of the trenches?

Measure your mind's height
by the shade it casts.
Robert Browning (Paracelsus)

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