Seaman's Handbook
ANNEX I. Positioning and technical details of lights and shapes
(a) The minimum luminous intensity of lights shall be calculated by using the
formula:
I = 3.43 X 166 X T2 X D X K-D
Where I is luminous intensity in candelas under service conditions,
T is threshold factor X 2 10-7 lux,
D is range of visibility (luminous range) of the lights in nautical miles,
K is atmospheric transmissivity.
For prescribed lights the value of K shall be 0.8, corresponding to a meteorological visibility of approximately 13 nautical
miles.(b) A selection of figures derived from the formula is given in the following table:
Range of visibility
(luminous range) of
light in nautical miles
D
Luminous intensity of
light in candelas for
K = 0.8
I
1 0.8
2 4.3
3 12
4 27
5 52
6 94
Note: The maximum luminous intensity of navigation lights should be limited to avoid undue glare. This shall not be
achieved by a variable control of luminous density.
