33 CFR 84.15: Horizontal sectors for navigation lights

Last reviewed: November 2, 2026

This section sets horizontal sector requirements for navigation lights. Forward sidelights must show minimum intensities and then cut off outside the prescribed sectors. Sternlights, masthead lights and sidelights at 22.5 degrees abaft the beam must keep minimum intensities up to 5 degrees within the sector limits. All-round lights may not be obscured within angular sectors of more than 6 degrees, with stated exceptions.

What it says

  1. In the forward direction, sidelights as fitted on the vessel must show the minimum required intensities.

    33 CFR 84.15(a)(i)“In the forward direction, sidelights as fitted on the vessel shall show the minimum required intensities.”

  2. In the forward direction, the intensities of sidelights must decrease to reach practical cut-off between 1 and 3 degrees outside the prescribed sectors.

    33 CFR 84.15(a)(i)“The intensities shall decrease to reach practical cut-off between 1 and 3 degrees outside the prescribed sectors.”

  3. For sternlights and masthead lights, and for sidelights at 22.5 degrees abaft the beam, the minimum required intensities must be maintained over the arc of the horizon up to 5 degrees within the limits of the sectors prescribed in Rule 21 (§ 83.21 of this chapter).

    33 CFR 84.15(a)(ii)“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”

  4. From 5 degrees within the prescribed sectors, intensity may decrease by 50 percent up to the prescribed limits. It must then decrease steadily to practical cut-off at not more than 5 degrees outside the prescribed sectors.

    33 CFR 84.15(a)(ii)“From 5 degrees within the prescribed sectors the intensity may decrease by 50 percent up to the prescribed limits;”

  5. All-round lights must be located so that masts, topmasts or structures do not obscure them within angular sectors of more than 6 degrees. Exceptions are anchor lights under Rule 30 (§ 83.30 of this chapter) and the all-round white light in Rule 23(e) (§ 83.23(e) of this chapter).

    33 CFR 84.15(b)(i)“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”

  6. The all-round white light described in Rule 23(e) (§ 83.23(e) of this chapter) may not be obscured at all.

    33 CFR 84.15(b)(i)“the all-round white light described in Rule 23(e) (§ 83.23(e) of this chapter), which may not be obscured at all.”

  7. If one all-round light cannot practicably meet paragraph (b)(i), two all-round lights must be used, suitably positioned or screened to appear, as far as practicable, as one light at a minimum distance of one nautical mile.

    33 CFR 84.15(b)(ii)“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.”

Common questions

How much may a mast obscure an all-round light?

An all-round light must not be obscured by masts, topmasts or structures within angular sectors of more than 6 degrees. Anchor lights under Rule 30 and the all-round white light in Rule 23(e) are treated differently.

“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”

When can I use two all-round lights instead of one?

Two all-round lights must be used if it is impracticable to comply with paragraph (b)(i) with only one. They must appear, as far as practicable, as one light at a minimum distance of one nautical mile.

“If it is impracticable to comply with paragraph (b)(i) of this section by exhibiting only one all-round light, two all-round lights shall be used”

How far apart can two unscreened all-round lights be and still look like one?

The note says two unscreened all-round lights that are 1.28 meters apart or less will appear as one light to the naked eye at a distance of one nautical mile.

“Two unscreened all-round lights that are 1.28 meters apart or less will appear as one light to the naked eye at a distance of one nautical mile.”

The text of 33 CFR 84.15

Electronic Code of Federal Regulations (eCFR), current as of April 16, 2026 · Read it on eCFR

Horizontal sectors

(a)(i) 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.

(ii) 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 (§ 83.21 of this chapter). 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 cut-off at not more than 5 degrees outside the prescribed sectors.

(b)(i) 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 (§ 83.30 of this chapter), which need not be placed at an impracticable height above the hull, and the all-round white light described in Rule 23(e) (§ 83.23(e) of this chapter), which may not be obscured at all.

(ii) If it is impracticable to comply with paragraph (b)(i) 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 1 to paragraph (b)(ii): Two unscreened all-round lights that are 1.28 meters apart or less will appear as one light to the naked eye at a distance of one nautical mile.

Sections it refers to

The plain-English explanation on this page was written with AI from the regulation text above and checked automatically before publishing: every quote appears in the text, every number comes from it, and a second model confirmed each statement adds nothing the text doesn't say. Regulation text current as of April 16, 2026. The regulation text governs. RegKnot is not affiliated with the U.S. Coast Guard.