What is the minimum visibility range of a masthead light in vessels of 50 meters or more in length

Using the following tables you can clarify the type(s) of navigation lights that are applicable to your vessel type and size.

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Required visibility in nautical miles (nm)
Visibility of Aqua Signal navigation lights in nautical miles (nm)
The range of Navigation lights
What Rule states the visibility of Navigation lights?
What is the range of Navigation lights in a vessel of 50 meters or more in length?
What is the range of Navigation lights in a vessel of 12 meters or more in length but less than 50 meters in length?
What is the range of Navigation lights in a vessel of less than 12 meters in length?
What is the range of Navigation lights of an inconspicuous, partly submerged vessel or object being towed?
The intensity of Navigation lights
The intensity formula
What do the parts of the Navigation light intensity formula mean?
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Please refer to the tables below to see what the definition of the IMO COLREGS 1972 is with regard to the relation between the requested visibility per type of navigation light and the length and type of boat or vessel where applied.

Example:
According to IMO COLREGS 1972, Aqua Signal series 34, 40, 41, 43 and 44 can be used on boats < 50m with only one exception, which is the masthead light since this one has to have 5 nm visibility instead of 3m (therefore the Aqua Signal Series 55 would be used on the Masthead in this case).

For regulations in various countries (if the craft will travel into international waters) please refer to the detailed approval list in this catalogue.

Please also cross-check your vessel type against our Navigation Lights User Guide to ensure you cover all of your navigation modes (e.g. a yacht must display a different navigation light array depending on whether it is sailing or under power

If you have any questions, feel free to contact your closest office to assist you.

Required visibility in nautical miles (nm)

Type of navigation light	Angle	Type of boat	Boats < 12m	Boats < 20m	Boats < 50m	Boats > 50m
Starboard	112.5°	Sailing & Motor boats	1 nm	2 nm	2 nm	3 nm
Port	112.5°	Sailing & Motor boats	1 nm	2 nm	2 nm	3 nm
Stern	135°	Sailing & Motor boats	2 nm	2 nm	2 nm	3 nm
Masthead	225°	Motor boats	2 nm	3 nm	5 nm	6 nm
All-round	360°	Sailing & Motor boats	2 nm	2 nm	2 nm	3 nm
Bi-colour	2 x 112.5°	Sailing & Motor boats	1 nm	2 nm
Tri-colour	2 x 112.5°+ 135°	Sailing boats	1-2 nm	2 nm

Type of navigation light	Angle	Type of boat	Series 20, 25	Series 34, 40, 41, 42, 43, 50	Series 55	Series 70, 70M, 70D
Starboard	112.5°	Sailing & Motor boats	1 nm	2 nm	2 nm	3 nm
Port	112.5°	Sailing & Motor boats	1 nm	2 nm	2 nm	3 nm
Stern	135°	Sailing & Motor boats	2 nm	2 nm	2 nm	3 nm
Masthead	225°	Motor boats	2 nm	3 nm	5 nm	6 nm
All-round	360°	Sailing & Motor boats	2 nm	2 nm	2 nm	3 nm
Bi-colour	2 x 112.5°	Sailing & Motor boats	1 nm	2 nm
Tri-colour	2 x 112.5°+ 135°	Sailing boats	1-2 nm	2 nm

Navsregs>COLREGS>Navigation Light Range

This post starts of with the simple facts of COLREG 22 and then delves deeper and deeper into definitions; deep into the world of lux, lumens and candelas.

Rule 22-visibility of lights

Note: This Rule states that navigation lights shall have an intensity as specified in Section 8 of Annex I to the COLREGS.

Masthead light- 6 miles
Sidelight-3 miles
Sternlight-3 miles
Towing light-3 miles
A white, red, green or yellow all-round light-3 miles

Masthead light, 5 miles; except that where the length of the vessel is less than 20 meters, 3 miles
Sidelight- 2 miles
Sternlight-2 miles;
Towing light-2 miles;
White, red, green or yellow all-round light-2 miles

Masthead light- 2 miles
Sidelight- 1 mile
A sternlight- 2 miles
Towing light-2 miles
White, red, green or yellow all-round light- 2 miles

White all-round light- 3 miles.

The intensity required to achieve the minimum range is derived from a formula given in Section 8 of Annex I to the Colregs.

The intensity formula

1=3.43 × 1 06×T × D2 × K-D

I is luminous intensity in candelas under service conditions

The candela is the SI unit of luminous intensity. It is the luminous power per unit solid angle emitted by a point light source in a particular direction.

Or to be more accurate, it is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

The steradian is a square radian, and is the SI unit of solid angle.

T is threshold factor 2 × 10-7 lux

The lux is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area.It is equal to one lumen per square metre. It is used as a measure of the intensity, as perceived by the human eye.

The lumen is the SI unit of luminous flux, a measure of the total quantity of visible light emitted by a source.

D is range of visibility (luminous range) of the light in nautical miles

The luminous range is the maximum distance at which a light can be seen, as determined by the luminous intensity of the light, the atmospheric transmission factor and the threshold of illuminance on the eye of the observer.

K is atmospheric transmissivity.

Atmospheric transmissivity is he ratio of the directly transmitted flux incident on a surface after passing through unit thickness of the atmosphere to the flux that would be incident on the same surface if the flux had passed through a vacuum.

The value of K shall be 0.8, corresponding to a meteorological visibility of approximately 13 nautical miles.