The biological basis for this complementary color effect is not well understood, nor is the depth of shadow, which is also an illusion.

CNN: What the brain draws from: Art and neuroscience

With delicate observation and quietly intense pathos, Dreyer captures the actors in a dappled light and a depth of shadow that seem to illuminate his characters from within.

NEWYORKER: The Parson's Widow

Since atoms have well understood light absorption properties, predictions can be made about the depth of a shadow cast, improving communication between the individual atoms performing calculations.

ENGADGET: Researchers capture a single atom's shadow, has implications for quantum computers