What Do the Red and Green Lights on Ships Really Mean?

Most people don’t think twice about those little red and green lights they see on a ship or boat.

They are, in fact, crucial for ship safety, especially at night or in bad weather.

This system of lights helps ships to avoid crashing into each other at night.

These lights are situated in the same position on every vessel to keep things constant and avoid any confusion.

History Of Navigational Lights

The United Kingdom passed the Steam Navigation Act of 1846, enabling the Lord High Admiral to publish new regulations requiring all sea-going steam vessels to carry lights.

From 1848 onwards, the Admiralty required steam vessels to display red and green sidelights, as well as a white masthead light whilst sailing, and a single white light when at anchor.

The 1948 International Safety of Life at Sea Conference recommended a mandatory second masthead light for power-driven vessels over 150 feet (46 m) in length and a fixed stern light for almost all vessels. The regulations have changed little since then.

In 1972, COLREGs (International Regulations for Preventing Collisions at Sea) laid down 41 rules that specify the types, colours, and positioning of navigation lights on ships. All vessels must obey these rules.

These rules ensure clear communication and safe navigation, particularly at night. They apply from sunset to sunrise and in restricted visibility.

What Do the Red and Green Lights Mean?

The position of these lights makes it easier to see from a distance which way a ship is travelling at night, or in bad weather.

These lights are fitted with a screen to prevent them from being seen on the other side of the ship, which could cause confusion.

• Red light = these are on the ship’s port side (left)
• Green light = These are on the ship’s starboard side (right)
  • These are always in the same place on every ship to keep things consistent.

Why Are They Important?

When one ship sees another at night, the colour tells them which side of the other ship they’re looking at.

It helps determine who has the right of way and how to avoid a collision.

For example, if you see a red light, you’re looking at the ship’s left side, and they might have the right of way.

There are strict rules about who has the right of way on the water. This is a very simplified view:

• Overtaking another ship:
  • The ship that is being overtaken is the “stand-on” vessel and it should continue its course and speed, while the overtaking ship (the “give-way” vessel) must take action to avoid them.
• Crossing each other’s path:
  • If two ships are crossing paths and there’s a risk of collision, the ship on the other’s starboard side must give way and avoid crossing ahead of the other. 
• Using Inland Waterways, like canals:
  • The boat coming downstream has the right of way. Under bridges, the boat closest to the bridge has the right of way. 
• On Rivers or Channels:
  • On rivers or channels, the ship should keep to the right-hand side (starboard) and pass oncoming traffic port to port (left to left). 

Other Navigation Lights You’ll See on Ships

• White light at the back = stern light
• White light on top = masthead light, shows direction and speed.
• Yellow flashing lights on some vessels = towing, special duties, etc.
• Cruise ships and large vessels have more complex arrangements, but the red/green basics are universal.

Who Decides these Rules?

These lights are part of the COLREGs (International Regulations for Preventing Collisions at Sea)

Lighting rules apply to all kinds of ships, from yachts to cruise ships.

Where Else Are These Coloured Lights Used?

Red/green lighting is also used in aviation, and even some spacecraft. This is thought to follow on from the original, well-known maritime rules.

Interestingly….

I once sailed on a river ship that had been in a collision with an MSC cruise ship – and survived!

This accident wasn’t caused by darkness or weather conditions; it was caused by “a combination of technical issues and potential human error.” 

The repairs cost over €3 million and took about three months to complete. The ship was out of service for an entire summer season, and fourteen river cruises were cancelled.

Find out what I thought of the ship when I sailed on her here:

Before You Go

Find out why ships are painted red underneath the waterline:

Why Are Ships Red Below The Waterline? – I Went Under One to Find Out!

Find out why some cruise ships have been cut in half here:

These Cruise Ships Were Cut in Half: Why and How (Royal, MSC, NCL & More)