I want to make certain shadows more prominent (using Cycles) without further illuminating the rest of the scene.
Example: I have a simple studio with a bowl of fruit and 3-point lighting. The light looks great so I don't want to change it but I want the bowl to cast a darker shadow on the ground (without dimming the back-light).
Alternatively, and this would be really cool, an anti-light source. Like a spot light that throws darkness instead of light. (Am I crazy for wanting this?)