What is the meaning of "restricted visibility"?

"Restricted visibility" refers to a situation where the visual range is significantly reduced, most commonly due to weather conditions such as fog, rain, snow, or mist. This reduced visibility can impede a mariner's ability to see other vessels, navigational aids, and the surrounding environment, greatly affecting safe navigation.

In maritime terms, restricted visibility is often defined in the context of a visual range that is below a certain measurement, indicating that navigational caution is required. This definition implies that navigators must be vigilant and often rely more on radar, sound signals, and other navigational aids when visibility is impaired.

The other options do not accurately capture the essence of restricted visibility. Clear visual range represents optimal conditions, optimal visibility does not align with the definition of restriction, and visibility only during daylight does not account for nighttime conditions that can also lead to reduced visibility due to weather leads to fewer options for mariners.