Select Page

How do navigators identify the different types of light around our coasts at night and what are their characteristics?

Navigating at night is made possible through an assortment of navigation aids, both ancient and modern. Lights are arguably the most important of these. Therefore, navigators need to be able identify the different types of light and what they signify. 

Electronic instruments help pinpoint a boat’s position, heading and speed. However, in order to be able to steer a safe and accurate passage, navigators must look out for and recognise the lights of navigation marks, beacons and lighthouses along their route.

How are lights identified?

Trying to identify every light you see can be difficult, especially when entering a harbour at night. In order to help with identification, each type has three main features:

  • Colour – green, red and white are most common. Yellow, blue, orange and purple are also sometimes used. 
  • Character – the rhythm of the light, or the flashing pattern it makes. 
  • Period – the length of time the light’s flashing sequence takes in seconds.

Learn all about buoyage and lights in our reference app IALA Buoys & Lights at Sea for all navigators at sea. The app includes a quiz to test yourself.

Light characteristics

Unless you are unfortunately colour blind, identifying the colour of lights is not too challenging. However, identifying a light’s character and the length of time its flashing sequence takes requires good night vision and concentration.

There are a number of light patterns which are used. Navigators need to learn the different types and their chart abbreviations in order to interpret charts correctly and to recognise lights. They include:

  • Fixed (F) – a single steady light. Often 2 together.
  • Occulting (Oc) – long periods of light with short periods of darkness. This has the effect of making the periods of darkness seem like flashes. 
  • Isophase (Iso) – equal periods of light and dark.
  • Flashing (Fl) – short periods of light with long periods of darkness. Eg Fl(3) flashes in groups of three and then a period of darkness.
  • Quick (Q) – quick flashes of light varying from 50 to 300 flashes per minute.
  • Alternating (Al) – a light with different colours of alternating light. Eg (Al RG) alternating red and green lights.
  • Morse code (Mo) – lights that flash a Morse code letter.

Tip: 

Time several light sequences with a stopwatch to confirm you have identified a light correctly.

Classes of lights and their abbreviations

Learn all about buoyage and lights in our reference app IALA Buoys & Lights at Sea for all navigators at sea.  The app includes a quiz to test yourself.

Light abbreviations

Charts, almanacs and pilot guides use abbreviations to describe lights A typical light characteristic, including its height above sea level and range is condensed into a few letters and numbers. Here is an example together with its meaning explained:

Fl(4) WRG 20s 23m 25M

FL(4)   Character of light: regularly repeating a group of 4 flashes.

WRG   Colours of light: white, red and green. If no colour is given then the light is white.

20s   Period of time taken to exhibit one full sequence: 20 seconds.

23m   Height of light above MHWS: 23 metres.

25M   Luminous range  the distance at which the light can be seen: 25 nautical miles.

Learn all about buoyage and lights in our reference app IALA Buoys & Lights at Sea for all navigators at sea.  The app includes a quiz to test yourself.

Happy boating and stay safe on the water!

The give-way hierarchy – sail boats and power boats

Who gives way to who at sea? Even seasoned sailors sometimes get this wrong and in a crowded harbour this can easily lead to a collision or at best considerable embarrassment for a boat that mistakenly thinks it has right of way over another.

Essential Yachting + Power Boat Safety Briefing

Yachting Safety Briefing   Down below Lifejackets and harnesses - fitting, when to wear, clipping on Gas - risks, precautions, gas bottles and...

First aid at sea basics

At least one person on board should be trained in first aid and know how to administer the contents of the first aid kit, ensuring there are adequate supplies for the planned duration of the trip.

Getting a tow for your sail or power boat at sea or on inland waterways

FREE tips from the Safe Skipper App for iPhone/iPad/Android: Getting a tow for your sail or power boat Plan how to secure a...

Essential Knots: Reef knot

Essential Knots: Reef knot Use: Tying two ends of rope together, often used for tying up a bundle of loose sail around the boom. Step...

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 9 – Around the Azores

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the ninth of a 10-part post where solo sailor, Bernie Branfield, shares his first-hand account of his single-handed, 2022 Jester Challenge, from Plymouth, UK to the Azores, in his 26′ Invicta Mk2, Louisa.

How to use tides and currents to your advantage

If you are contemplating a cruise through tidal waters and strong currents, then planning your trip carefully in advance is essential to enable you to take advantage of favourable tides rather than constantly fighting against them.

Tidal heights and the rule of twelfths

For those skippers who need to make a quick calculation or don’t have access to specific tidal curves for their location, it is possible to make an approximation using a system called the Rule of Twelfths. This is a simple method used to estimate the height of tide at any given time during the tidal cycle. It is based on the idea that the rise and fall of the tide is not constant, but follows a predictable pattern than can be divided into twelve parts.

Boating emergency – how to broadcast a MAYDAY emergency call

How to broadcast a MAYDAY emergency call   How to broadcast a MAYDAY emergency call if a vessel or person is in grave...

Wooden Hull Repairs

While wooden boat hull maintenance is mostly straightforward, it is always a good idea to take expert advice on any repair job needed doing to a wooden boat, unless you have done the job before and know what you are doing.

How to improve a yacht’s upwind performance

There are several ways to improve the upwind performance of a sailing yacht. Read on for some useful tips including headsail reefing, heavy weather jibs and motor sailing.

Understanding marine sealants & adhesives

Sealants, adhesives and adhesive sealantsThere is a bewildering variety of sealants, adhesives and even adhesive sealants available for...

Pleasure craft safety equipment recommendations

Safety equipment is an important part of boat preparation and it is advisable for all pleasure craft skippers to check their vessel is...

Marine toilets – care and maintenance

There are a number of different types of marine toilet, or heads. They fall into one of three categories – manual, electric and vacuum, the most common being the manual, hand pumped type. These have double acting piston-pumps which both discharge the waste and flush the toilet with sea water.

Cutless bearing replacement

Cutless bearings can last for many years but if the propeller shaft is out of alignment they will wear through more quickly. If you have noticed a clunking sound when motoring then it could be a worn cutless bearing that is causing the problem.

Learning about diesel engine maintenance

Marine diesel engines are internal combustion engines that are designed specifically for use in maritime applications. These engines are commonly used in a variety of watercraft, ranging from small boats and yachts to large ships and vessels. Learn about marine diesel engine maintenance courses.

Care of boat batteries

Boat batteries need to be kept properly charged, which means never allowing the batteries to discharge below 50 per cent of their total charge. As well as the batteries themselves, keeping a boat’s charging systems in good shape will also help to keep batteries topped up to a higher level of charge.

Peer to Peer yacht charter – How can you monetize your boat?

There is a growing trend in peer to peer yacht charter. How does it work? People already rent rooms, cars and bikes from one...

Boat batteries

Under-sized battery banks are one of the key factors behind power failure at sea, as well as the premature failure of batteries, so make sure that your boat battery measures up to the use you want to put it to.

ColRegs when sailing single handed

  Don’t neglect the Colregs when sailing single handed Sailing single-handed represents several challenges for skippers, not least how to...

Learn ColRegs: Traffic Separation Schemes

Learn ColRegs Rule 10: Traffic Separation Schemes. (c) A vessel shall, so far as practicable, avoid crossing traffic lanes...

Understanding tides

If you are used to sailing in tidal waters, you will know that tides can be both a benefit and a hindrance to the sailor. In many ways,...

ColRegs – avoiding collisions at sea

ColRegs - avoiding collisions at sea ColRegs Rule 8: Action to avoid collision (a) Any action taken to avoid collision shall...

Gybing a sailing boat

Gybing is the sailing manoeuvre used to change a boat's direction through a following wind. As with the tacking manoeuvre,...

Man Overboard Drill

How to respond to crew overboard under sail • Keep the MOB in sight • Tack into the heave-to position, do not adjust the...