Bilateral navigation lights refer to two symmetrical navigation lights on a vessel's port (red) and starboard (green) sides . These lights help other vessels determine a vessel's direction and orientation , especially when sailing at night or in poor visibility .
1. Features of bilateral side lighting
✅ Consists of a port light (red) and a starboard light (green) → Helps other vessels to recognize the position and direction of travel .
✅ Shines in an arc of 112.5° → Visible from straight ahead to 22.5° abaft the ship's beam .
✅ Mandatory for night sailing or poor visibility → Must burn between sunset and sunrise .
✅ Placed on the sides of the vessel → Usually on the bow or hull, or integrated into the mast for smaller vessels.
✅ Visibility at least 2 nautical miles → Depending on the size and type of vessel.
2. Function of bilateral side lighting
📌 Provides other vessels with insight into your direction of travel → When you see a red light , look to port ; when you see a green light , look to starboard .
📌 Essential for applying international navigation regulations → Prevents collisions and helps determine right of way.
📌 Part of a ship's basic navigation system → Works in conjunction with the stern light (white) and possibly the masthead light (white) .
3. When is bilateral side lighting mandatory?
According to the International Regulations for Preventing Collisions at Sea (COLREGS), the following ships are required to carry bilateral side lights:
| Ship length | Obligation |
|---|---|
| < 7 meters (23 ft) | May be replaced by one white all-round light . |
| 7 - 20 meters (23 - 65 ft) | Mandatory : Port light + Starboard light + Stern light. |
| > 20 meters (65+ ft) | Mandatory : Port light + Starboard light + Stern light + Mast light. |
| Sailboats under sail | Mandatory : Port and starboard lights (or a three-colour masthead light). |
⛵ Sailing vessels may carry a tricolour light on the mast instead of separate sidelights .
4. Difference between Bilateral Side Lights and other Navigation Lights
| Light type | Goal | Colour | Corner |
|---|---|---|---|
| Bilateral Sidelights | Indicates the port and starboard sides of a vessel | Red (port), Green (starboard) | 112.5° |
| Stern Light | Shows the rear of the ship | White | 135° |
| Masthead Light | Indicates that a vessel is operating under motor | White | 225° |
| Anchor light | Shows an anchored ship | White | 360° around |
💡 Tip: When you see a green and a red light on the water, a ship is coming straight towards you.
5. Types of bilateral side lighting
🔹 LED side lights → Energy-efficient, long life.
🔹 12V / 24V navigation lights → For motorboats and yachts.
🔹 Portable Navigation Lights → For small boats and kayaks.
🔹 Combination lights → A single unit with both port and starboard lights.
💡 In short:
Bilateral navigation lights, consisting of a red (port) and green (starboard) navigation light , are mandatory for all vessels sailing at night . These lights help to determine a vessel's direction of travel and contribute to safety and compliance with international navigation regulations .