The International Regulations for Preventing Collisions at Sea (COLREGs) set out mandatory requirements for navigation lights, ensuring vessels can be seen at appropriate distances during night or reduced‑visibility conditions.
One key factor influencing the required visibility range is the length of the vessel. Longer vessels present a larger target and therefore must be visible from a greater distance to give other mariners sufficient reaction time.
L = vessel length (metres)
Use the calculator below to enter your vessel’s length and select the appropriate light category. The result will show the minimum distance at which the navigation lights must be visible according to the simplified COLREGs guideline.
How do I calculate the visibility range for my vessel’s navigation lights?
What is the purpose of COLREGs navigation lights?
Why do longer vessels need a greater visibility range?
Can I use this calculator for any type of vessel?
What is the unit for the visibility range D?
Is this formula applicable to all types of navigation lights?
How often should I check and adjust my vessel’s navigation lights?
Results are for informational purposes only and do not constitute professional advice.