§ 84.14 Intensity of lights

(a) The minimum luminous intensity of lights shall be calculated by using the formula:

I = 3.43 × 10 6 × T × D 2 × K−D

Where:

I is luminous intensity in candelas under service conditions,

T is threshold factor 2 × 10−7lux,

D is range of visibility (luminous range) of the light 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 (Table 84.14(b)):

Range of visibility(luminous range) of lightin nautical miles D	Minimum luminous intensity of light in candelas for K = 0.8 I
1	0.9
2	4.3
3	12
4	27
5	52
6	94

US Inland Navigation Rules current as of 22 October 2026. Official text: ecfr.gov.

A work of the US government, in the public domain. Reproduced from the eCFR (ecfr.gov), 33 CFR parts 83 to 88.