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.