Under which type of conditions do both photopic and scotopic systems operate?

The correct choice is the scenario involving dim lighting at dusk. This environment is characterized by reduced light levels, making it a transitional time when both photopic and scotopic vision systems are actively engaged.

The photopic system, which operates through cone photoreceptors, is responsible for vision under well-lit conditions and facilitates tasks like color discrimination and fine detail recognition. Meanwhile, the scotopic system, which relies on rod photoreceptors, is optimized for low-light conditions and is more sensitive to light, allowing for vision when illumination is minimal.

At dusk, light levels decrease gradually enough that both systems are needed for optimal vision. The cones begin to lose their sensitivity while rods activate to allow vision in lower light. This simultaneous activation helps individuals navigate and maintain functionality in the changing light environment.

In contrast, under bright sunlight, primarily the photopic system is engaged due to the high light levels, while in complete darkness, only the scotopic system is functional, as there is insufficient light for either system to provide visual input. Fluorescent lighting can vary widely in brightness, but it is typically more uniform and brightly lit than the dim light at dusk.