Lighthouses are iconic seaside signalling spires that have guided mariners ‘round
the twists and turns of dangerous coastal obstacles for millennia.
But how do they actually work?
And what on earth is this?
Let’s jump in and find out – and make sure you stick around for the whole video,
as we talk to a real lighthouse keeper.
First off, a little bit of history.
Lights on shore help sailors safely navigate the ocean.
The earliest lighthouses used wood or coal fires.
But it’s obviously not ideal to lug fuel to the top of a tower every day.
Next were candles, gas lamps and oil lamps.
But firelight isn’t actually that bright, and as you can imagine, fires inside tall
structures is a major safety hazard, so when electricity was discovered, lighthouses began
switching to electric bulbs, which were brighter, and which is what most lighthouses use today.
So how do lighthouses actually direct that light far out to sea where it can be seen
by ships?
In many cases, the answer is this beautiful structure – the Fresnel lens.
Up until the 1800s, lighthouses had used reflectors behind the light source to direct the light
outwards.
Clever engineers realised that light could also be further focussed using a lens in front
of the light source.
The problem with this idea, is that a lens large enough to gather all of this light would
have to be huge – not ideal for the top of a tower.
Not to mention, the larger and thicker the lens, the more light is absorbed by the glass
itself when the light passes through.
So, in the early 1820s, Fresnel, a French physicist and engineer, came up with a very
elegant solution.
Fresnel knew that light is refracted at the point at which it passes from one medium to
another, in this case from air to glass and back to air, and that the curved surface of
the lens that focusses the light in the desired direction – so he simply cut away the rest
of the lens.
He brought down the surface of the lens in stepped sections, so that the curve of the
surface was preserved, and the excess internal material was discarded.
This allowed for light to be focussed in a particular direction, while reducing absorption
of light by the lens itself, because the lens wasn’t as thick.
While Fresnel wasn’t the first person ever to propose this kind of prism, he certainly
pioneered developments of the eponymous stepped lens.
Shortly after this innovation, extra prisms were added to the top and bottom of the lens,
so that it could catch and redirect even more light.
Fresnel lenses come in all shapes and sizes, from the smaller 6th order lenses, all the
way up to 1st order lenses and even hyper radiant lenses, like the one at the Makapu’u
Point Lighthouse, which is insanely big.
This invention revolutionised lighthouses, and made them even better at their job.
By redirecting more light they could be seen from an even further distance away.
So that brings us to their main function, signalling.
A lighthouse’s utility depends on the geography surrounding it.
Some lighthouses are near dangerous rocks, and others near safe entrances to harbours.
Vessels can triangulate their own position relative to the known position of lights on
shore.
Lighthouses can use a series of flashes, and sometimes different colours, to identify themselves
to mariners – this is called a light characteristic.
Many lighthouses have an individual (though not necessarily unique) light characteristic.
For example, the Split Point lighthouse in Australia has a light characteristic of 4
white flashes over 20 seconds.
A flash is when the light is bright only for a short time.
In comparison to an occulting light, which is when the light is dark for a short time.
Using a combination of these different light types, with different timings and different
colours, means there is an infinite number of potential light characteristics.
So, let’s find out what’s inside the lantern room, right at the top, as we talk about how
these flashes of light are generated.
This part of the video has heaps of incredibly beautiful Fresnel lenses – mostly thanks
to Artworks Florida, a company that actually makes and restores Fresnel lenses – there’ll
be a link to their channel below.
Some lighthouses have a rotating lens, made up of several bullseye-like Fresnel lenses.
As each lens rotates around the light source, the bullseyes beam light out in a single direction.
As the narrow beam of light sweeps across the ocean – from a ship, it looks like the
light is flashing.
In reality the light is always on, and it is the rotation of the lens that gives the
flashing effect.
Some lighthouses use a Fresnel lens with a belt-like centre.
In this case, the lens can be in a fixed position, and the light itself turns on and off, and
the lens directs the flashing light in a wide angle.
Again, from a ship it looks like a flashing light, but this time because it is a flashing
light.
But flashes aren’t the only way lighthouses communicate.
Some lighthouses use coloured filters to change the colour of the light depending on the angle
that they are viewed from.
For example, this lighthouse has red filters on the far left and far right – also note
the opaque paint to stop the light from flashing backwards, onto the land.
When viewed from these directions, mariners will know that they may be approaching unsafe
rocks.
You might have noticed that the Cape Byron lighthouse at Byron Bay, Australia has 2 light
characteristics – that’s because it’s normal characteristic is a flashing white
light, but it also has a secondary light, that shines a fixed beam of red light towards
some dangerous rocks nearby.
Some lighthouses also signal during the day, using daymarks.
These distinctive markings make it easy for lighthouses to be identified during the day,
again aiding navigation.
Before telecommunication and GPS, lighthouses could also signal with flags during the day,
and Morse-coded lights at night – but these methods are somewhat obsolete today.
Of course, many lighthouses don’t quite look like the romantic buildings of old, and
many now use LED lights, or directional lighting systems other than Fresnel lenses – like
this tower with a rotating light.
In fact, when I visited this tower on a recent trip, it got me thinking – since this tower
doesn’t have a lantern room at the top, can we call it a lighthouse?
What makes a lighthouse, a lighthouse, compared to any other coastal lights?
To help us answer that question, I asked a modern day lighthouse keeper.
Hi, my name is Spence, and I’m a modern-day lighthouse keeper.
We’re going to talk a little bit about what makes a lighthouse a lighthouse, and how they
may differ from an actual light station.
Now there are many different aids to navigation.
Everything from buoys, to beacons, and sector lights, and lighthouses.
Lighthouses, typically, are tall cylindrical structures, with a cupola on top and a beacon
or a light inside, which flashes light, helping show mariners where they are on the water.
Another such important light is what they call a sector light.
Now a sector light is a light which helps to guide mariners through a channel or a more
dangerous area where they may be transferring from one channel to another and there’s
a difficult curve or difficult area to navigate.
So what about a light station?
A light station is a base of operations that the Coast Guard can use that usually has a
lighthouse or a sector light, or another very important light that’s used in navigation.
Now a light station will have many different buildings.
Including a dwelling for a lightkeeper to live in, maybe a workshop, and engine room
for providing power and a boathouse, dock, radio room.
There’s all kinds of different areas on the station that can be used by the keepers,
or by Coast Guard personnel in case of an emergency.
Or even by mariners who are in a state of emergency and need to go to a light station
for aid.
I hope you found this information helpful, and it provided you a little more insight
into what makes a light house, what makes a light station, and what it’s like to be
a lighthouse keeper.
Thanks Spence!
You should all definitely check out his YouTube channel for incredible insights into the life
of a lighthouse keeper – links at the end of the video.
Given that this particular lighthouse did used to have a lantern room, I think we can
still call it a lighthouse.
Many lighthouses now run on solar power, or batteries with generators, or a combination
of both.
This has reduced the need for permanent lighthouse keepers, although of course they do still
exist in some places – and are important for weather observations, light station maintenance
and emergency responses among other things.
Of those lighthouses that do still use Fresnel lenses, some have transitioned to cheaper
and more modern acrylic lenses.
But the purpose of lighthouses remains the same, a focussed beacon of light, not to illuminate,
but to signal.
So, that’s how lighthouses work.
They have a light source that can be fixed with a rotating lens, or flashing with a fixed
lens.
This is beamed seawards, and creates the lighthouse’s light characteristic, which identifies it
to anyone navigating the ocean.
In the current era, when many ships primarily use the Global Positioning System to navigate,
lighthouses may not be as relied on as they once were, but they still do serve a vital
role in maritime safety.
I’ll play you out with this special tune thanks to Andrew Duffield, and thanks again
to Artworks Florida and to Spence the lighthouse keeper for being a part of this video, please
do check out both of their channels if lighthouses interest you.
And thanks to you for being here until right at the end.
I’ll see you next time.