Which object is most suitable for determining nighttime visibility?

To determine nighttime visibility effectively, the most suitable option involves unfocused lights of moderate intensity at known distances. This is because such lights provide a practical and realistic simulation of how visibility conditions appear in the dark. Unfocused lights help to create a more diffuse and widespread illumination that mimics natural light conditions, making it easier to assess how far one can see under nighttime circumstances.

Using unfocused lights allows observers to gauge visibility without the glare or distraction that focused or intense lights can cause. In essence, moderate intensity ensures that the lights are not overwhelming, aiding in the assessment of how visibility diminishes in low-light conditions. This approach aligns well with the methods used in real-world observations, making it a preferred choice for evaluating nighttime visibility.

The other choices involve lights that either may not accurately represent visibility conditions or are less practical for such assessments. Searchlights, for instance, are designed to illuminate specific areas rather than providing a general sense of visibility. High-intensity runway lights, while effective for guiding pilots, could create glare that hinders visibility assessments when considering how far one can see at night. Focused lights, although they provide targeted illumination, do not take into account the diffuse visibility that one needs to assess overall nighttime conditions. Therefore, unfocused