Sidelights (Port & Starboard Navigation Lights)
Definition of Sidelights
Sidelights are the red and green navigation lights visible from the front (bow) and sides of a boat when it is underway at night (sunset to sunrise). These lights are positioned to shine continuously over an arc of 112.5° on each side of the vessel – from directly ahead to 22.5° abaft the beam (just behind the boat’s widest point) on their respective side. Because of this placement, sidelights are only visible to approaching vessels from the front or side of your boat, not from behind.
The two colors of sidelights indicate which side of the boat is visible:
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Red sidelight: Marks the port side (the left side of the boat when facing forward).
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Green sidelight: Marks the starboard side (the right side of the boat when facing forward).
In other words, if another vessel sees a red light, they are looking at your boat’s port side; if they see green, they are looking at the starboard side. This color code helps boaters determine right-of-way at night. Generally, you must give way if you see a red light (indicating you are approaching the port side of another vessel) and stand on (maintain your course) if you see green (indicating you are approaching their starboard side).
Visibility and Arc: To achieve the uninterrupted 112.5° arc on each side, each sidelight shines from dead ahead to 22.5° past the beam toward the rear. (See illustration below.) Together, the port and starboard lights cover the forward 225° of the horizon, and they are not visible beyond that arc (so as not to be confused with the stern light).
Illustration: Top-view of a vessel showing the red port sidelight and green starboard sidelight, each covering 112.5° from the bow. The white stern light (135°) covers the remaining arc behind the vessel.
Navigation Light Requirements by Boat Size
The sidelights required – and whether they can be combined or must be separate – depend on your boat’s size and type (sail or power). The visibility distance of the lights (how far away they must be seen) also increases for larger vessels. Below is a breakdown of sidelight requirements:
| Boat Type & Length | Sidelight Configuration | Minimum Visibility |
|---|---|---|
| Sailboat (under sail, no motor) |
Under 23 ft (7 m): Sidelights recommended but not required (carry a white light/flashlight as a substitute). 23–65 ft (7–20 m): Separate port and starboard sidelights or a combined red/green bi-color bow light imtra.com. Over 65 ft (20 m): Separate sidelights (one red, one green, each side). |
Under 23 ft: 1 NM 23–65 ft: 1 NM Over 65 ft: 2 NM |
| Powerboat (or sailboat under power) |
Under 23 ft (7 m): May use a combined bi-color bow light (red/green) if practicable, plus a 360° white light (all-around light). 23–165 ft (7–50 m): Must show separate red and green sidelights (or combined bi-color for vessels under 65.6 ft). |
Under 23 ft: 2 NM* Over 23 ft: 2 NM |
<small>*NM = nautical miles. *Small powerboats under 23 ft going under 7 knots may show just an all-around white light, but using sidelights is strongly recommended for visibility.</small>
For sailboats, there is an additional option when sailing under 65 ft: you may use a tri-color masthead light instead of separate sidelights + stern light. A tri-color navigation light (showing red, green, and white in one fixture) is mounted at the top of the mast and covers all three directions – red to port, green to starboard, and white to the rear – in a single lamp. Important: Tri-color lights are only used under sail; if you turn on the engine, you must switch to the standard sidelights (and masthead light for power) configuration for compliance.
Examples of Sidelight Products (Brands & Options)
Modern marine sidelights are almost always LED for longevity and low power draw. They come in various styles (horizontal or vertical mount, separate fixtures, or combined bi-color lights) to fit different boats. Here are a few examples of sidelights available from DRSA (with product links):
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Hella Marine NaviLED LED Sidelights (Port & Starboard, 2 NM): A compact pair of red/green LED sidelights for power or sail boats. Extremely energy-efficient and waterproof (IP67) for reliable service (Example: Hella NaviLED Port & Starboard 2NM Kit, Black Housing.)
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Perko 2 NM LED Bi-Color Light: A single bow-mounted fixture combining port and starboard lights, ideal for smaller vessels. Modern LED design with classic styling and 2-mile visibility. (Example: Perko 12V LED Bi-Color Navigation Light, Black/Stainless.)
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Lopolight 2 NM LED Sidelights (Vertical Mount): High-end anodized aluminum sidelights for yachts up to 50 m. Sold as separate port or starboard units; ultra-compact with a sleek vertical mount design. (Example: Lopolight Series 301-001 LED Starboard Sidelight, 2NM, vertical mount.)
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Sea-Dog Stainless LED Side-Mount Lights (Pair): Economical port/starboard light set in polished stainless steel housings. Mounts to the vertical sides of the bow. USCG-approved 2 NM visibility for boats under 20 m. (Example: Sea-Dog 2 NM Port/Starboard Side-Mount LED Nav Lights, #400079-1.)