Anyone who falls overboard at night can easily be lost from view, even amongst small waves. A lifejacket light is designed to make the person visible to the crew searching for them. It complements the high-visibility colour and reflective strips. To raise the alarm and pinpoint the person’s location, it is also possible to Emergency radio for use at sea contribute. But how far does the light from a high-visibility vest actually reach?
The LED comes out on top in the laboratory
For their research report, the Federal Maritime and Hydrographic Agency (BSH) and the German Maritime Search and Rescue Service (DGzRS) compared two approved life jacket lights: one with an LED, the other with an incandescent bulb. At room temperature, the LED achieved an effective luminous intensity of 1.71 candelas, whilst the incandescent bulb achieved 1.27 candelas. A candela describes the luminous intensity in a specific direction. Even at 6 and 14 degrees – corresponding to the water temperatures used in the tests – the LED came out on top.
Both lights exceeded the prescribed minimum luminous intensity of 0.75 candela. Even on land, the LED appeared brighter and was visible from a greater distance. Based on these results, it should also have been the first to be noticed at sea.
At sea, the picture changes
For the night-time trials, the researchers attached the lights to freely drifting test objects and fitted them with AIS transponders. Vessels from the BSH and DGzRS approached in a search formation. Several observers noted when they first saw each flashing light.
In three out of four tests, they detected the incandescent light from a greater distance than the LED. Only once did the model that was stronger in the laboratory come out on top. In photographs taken during one test from a distance of 445 metres, the incandescent light appeared larger and slightly brighter. The research report does not specify the manufacturers or model names of the lights compared.
The two organisations are jointly investigating the visibility of rescue equipment. Just above the water’s surface, it is not solely the laboratory reading that determines what a search team perceives.
Why did the incandescent light bulb stand out in the past?
The cause remains unclear. LEDs and incandescent bulbs produce light with different spectral compositions. One hypothesis put forward by the researchers is that spray, foam, moisture and waves could scatter or attenuate individual components of the light to varying degrees just above the water’s surface. This would explain why a light might be harder to see despite having a higher measured intensity. However, this correlation has not yet been proven.
The fact that the LED performed better on land supports this hypothesis. However, the only sea trial in which it was first detected took place closer to the coast and under different conditions. This, too, does not yet allow for a definitive explanation.
For boaters, the difference between the two lights tested does not constitute a verdict on all LED lights. Four sea trials and two models are not sufficient for that. Light colour and beam pattern may also vary from model to model. BSH and DGzRS therefore intend to investigate further light sources and conditions at sea.
In practical terms, it remains important that the light matches the lifejacket, fits correctly and is ready for use. A water-activated lifejacket light can improve visibility, but is no substitute for other search and rescue measures. When checking the Putting on and fastening the life jacket also the light, in accordance with the manufacturer’s instructions. Our guide shows how different vests differ from one another Comparison of automatic lifejackets.
Further articles on this topic
Our guide explains how tracking and alert systems complement search operations. System overview of emergency transmitters. The following demonstrates what a life jacket must be capable of, apart from having a signal light: Comparison of 24 automatic vests.
Book recommendations
Handbook for Motorboat Operators By Paul Glatzel, this book covers safety on board and the man-overboard manoeuvre as part of practical seamanship. Step-by-step colour illustrations make the procedures described easy to follow. The book helps you to go through not only the equipment but also the crew’s roles in an emergency before setting sail. It also explains navigation, the weather and other basics for everyday life on a motorboat.
Boats - Logbook Christian Tiedt’s book is designed as a handy companion for your sailing trip. Its concise chapters cover, amongst other things, safety on the water and how to behave in emergency situations, as well as navigation rules, marine radio and practical sailing tips. Whilst the Manoeuvres handbook explains these topics in greater detail, this logbook is intended more as a reference guide on board when you’re unsure about a particular rule or procedure.
Does your life jacket have a light? What did you look out for when buying it? Please share your thoughts in the comments.
Ursula Meer
Redakteurin Panorama und Reise