What is the correct sequence to determine Computed Visibility?

• A. Compute R_geo; Determine Nominal Range from literature; Determine Meteorological Visibility; Compute Luminous Range from graph; Compare Luminous Range to R_geo; The lesser is Computed Visibility.
• B. Compute Luminous Range; Determine Nominal Range; Compute R_geo; Determine Meteorological Visibility; Compare to R_geo.
• C. Determine Nominal Range; Compute R_geo; Compute Luminous Range; Determine Meteorological Visibility; Compare to R_geo.
• D. Compute R_geo; Compute Luminous Range; Determine Nominal Range; Determine Meteorological Visibility; The greater is Computed Visibility.

Answer: (A)

Computed Visibility is the distance at which a light is actually visible under current geometry and atmospheric conditions. The proper flow starts with the geometric range to the light, since you must know how far the light is in space from your position. Next, you consult the light’s Nominal Range from published data as a reference for the maximum distance the light could be seen under standard (ideal) conditions. Then you determine the prevailing meteorological visibility to understand how the atmosphere is limiting sighting. With that meteorological visibility, you read the Luminous Range from the light’s performance graph, which tells you how far the light should appear under the current conditions. Finally, you compare the Luminous Range to the geometric range and take the smaller distance as the Computed Visibility (the light cannot be seen beyond either the line‑of‑sight distance or the atmospheric/optical limit).