Both photopic and scotopic systems are active under which conditions?

The correct answer is mesopic conditions because this refers to lighting situations that are intermediate between bright daylight (photopic) and low-light conditions (scotopic). During mesopic lighting, both types of photoreceptors in the retina—rods and cones—are active simultaneously.

In photopic conditions, which are well-lit environments, the cone system predominates, as cones are primarily responsible for color vision and function best in bright light. Conversely, during scotopic conditions, which occur in dim or dark settings, the rod system is primarily engaged. Rods are highly sensitive to low light levels but do not detect color.

Under mesopic conditions, both rods and cones contribute to visual perception. This situation typically occurs at dawn or dusk or in poorly lit environments where some light is present but not sufficient for full cone function. This unique interplay allows for enhanced visual acuity and sensitivity, optimizing our ability to see in conditions with varying light levels.