Simultaneous brightness contrast occurs when:

Simultaneous brightness contrast is a perceptual phenomenon where the appearance of a target area is influenced by the brightness of its surrounding areas. When a target area is surrounded by different luminance levels, our visual system interprets the brightness of the target differently, leading to the perception that the same target area can look brighter or darker depending on what it's adjacent to. This is why option C is the best choice, as it accurately captures the essence of simultaneous brightness contrast.

In this situation, the perception of brightness does not depend solely on the target itself but is dynamically affected by the luminance of surrounding regions, leading to either an enhancement or reduction in perceived brightness. The other options do not fully encompass the nuance of this effect; they either describe aspects that are more reflective of static brightness or do not account for the simultaneous nature of this perceptual experience.