Crafting forms is all about placement of the terminator, first and foremost. Then you figure out what else is in the room for bounce light, and make any specular and translucency adjustments. boom.
The size of your light affects the position of the terminator. If a giant window is lighting a sphere, less than 50% of it will be in shadow. The strength of your light affects the speed of the gradient as the planes darken toward the terminator.
In a large light scenario, shadows have more value variation and are generally more gradient-like because of the bounce light.
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