Read Rule 20 carefully....
Here's what a nav light needs to comply with..
From 33 CFR 84:
Colors
� 84.13 Color specification of lights
(a) The chromaticity of all navigation lights shall conform to the following standards, which lie within the boundaries of the area of the diagram specified for each color by the International Commission on Illumination (CIE), in the "Colors of Light Signals", which is incorporated by reference. It is Publication CIE No. 2.2. (TC-1.6), 1975, and is available from the Illumination Engineering Society, 345 East 47th Street, New York, NY 10017. It is also available for inspection at the Office of the Federal Register, Room 8401, 1100 L Street N.W., Washington, D.C. 20408. This incorporation by reference was approved by the Director of the Federal Register.
(b) The boundaries of the area for each color are given by indicating the corner coordinates, which are as follows:
(1) White:
x 0.525 0.525 0.452 0.310 0.310 0.443
y 0.382 0.440 0.440 0.348 0.283 0.382
(2) Green:
x 0.028 0.009 0.300 0.203
y 0.385 0.723 0.511 0.356
(3) Red:
x 0.680 0.660 0.735 0.721
y 0.320 0.320 0.265 0.259
(4) Yellow:
x 0.612 0.618 0.575 0.575
y 0.382 0.382 0.425 0.406
Intensity
� 84.15 Intensity of lights
(a) The minimum luminous intensity of lights shall be calculated by using the formula:
l = 3.43 x 106 x T x D2 x K-D
where:
I is luminous intensity in candelas under service conditions, T is threshold factor 2 x 10-7 lux, 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 Table 84.15(b).
Table 84.15(b)
Range of visibility (luminous Minimum
range) of light in nautical luminous intensity of light
miles in candelas tor K = 0.8
D I
1 0.9
2 4.3
3 12
4 27
5 52
6 94
Horizontal Sectors
� 84.17 Horizontal sectors
(a)
(1) In the forward direction, sidelights as fitted on the vessel shall show the minimum required intensities. The intensities shall decrease to reach practical cut-off between 1 and 3 degrees outside the prescribed sectors.
(2) For sternlights and masthead lights and at 22.5 degrees abaft the beam for sidelights, the minimum required intensities shall be maintained over the arc of the horizon up to 5 degrees within the limits of the sectors prescribed in Rule 21. From 5 degrees within the prescribed sectors the intensity may decrease by 50 percent up to the prescribed limits; it shall decrease steadily to reach practical cutoff at not more than 5 degrees outside the prescribed sectors. (b) All-round lights shall be so located as not to be obscured by masts, topmasts or structures within angular sectors of more than 6 degrees, except anchor lights prescribed in Rule 30, which need not be placed at an impracticable height above the hull, and the all-round white light described in Rule 23(d), which may not be obscured at all. (c) If it is impracticable to comply with paragraph (b) of this section by exhibiting only one all-round light, two all-round lights shall be used suitably positioned or screened to appear, as far as practicable, as one light at a minimum distance of one nautical mile.
NOTE to paragraph (c): Two unscreened all-round lights that are 1.28 meters appart or less will appear as one light to the naked eye at a distance of one nautical mile.
Vertical Sectors
� 84.19 Vertical sectors
(a) The vertical sectors of electric lights as fitted, with the exception of lights on sailing vessels underway and on unmanned barges, shall ensure that:
(1) At least the required minimum intensity is maintained at all angles from 5 degrees above to 5 degrees below the horizontal;
(2) At least 60 percent of the required minimum intensity is maintained from 7.5 degrees above to 7.5 degrees below the horizontal.
(b) In the case of sailing vessels underway the vertical sectors of electric lights as fitted shall ensure that:
(1) At least the required minimum intensity is maintained at all angles from 5 degrees above to 5 degrees below the horizontal;
(2) At least 50 percent of the required minimum intensity is maintained from 25 degrees above to 25 degrees below the horizontal.
(c) In the case of unmanned barges the minimum required intensity of electric lights as fitted shall be maintained on the horizontal.
(d) In the case of lights other than electric lights these specifications shall be met as closely as possible.