I have visited a fair number of lighthouses and for a long time treated them as scenery. Understanding what they actually did, and why almost none of them do it in the same way now, made them considerably more interesting.
The problem they solved
A ship at night, before electronic navigation, had to know where it was relative to a coast that could destroy it.
A light solves that only if you can tell which light it is, which is the part people do not think about. A single light on a dark coast tells you almost nothing.
So every lighthouse was given a distinct character — a pattern of flashes and intervals unique within its area. A navigator with a chart and a watch could time the pattern and identify precisely which light they were looking at, and therefore where they were.
That is the actual technology. The brightness is engineering; the pattern is the information.
Many also have sectors, showing different colours in different directions, so that seeing red rather than white tells you that you are in a dangerous bearing.
The optics were the hard part
The technical achievement that impressed me most once I understood it.
A light source radiates in all directions, and most of that is wasted. The problem is concentrating it into a beam that travels a long way over water.
The solution developed in the nineteenth century was a stepped lens arrangement that collects light from a wide angle and bends it into a horizontal beam, achieving what a solid lens of the same power would achieve while being a fraction of the weight.
These assemblies are large, extremely heavy and beautifully made, and many float in a bath of mercury so that the whole thing can be rotated by a small clockwork mechanism.
Where they survive, they are worth seeing for their own sake. A lot were removed and scrapped during automation, which is a loss that people who care about such things still complain about.
What keepers actually did
Less romantic and more mechanical than the image suggests.
Maintaining the light source, which for most of the history meant tending a flame — trimming wicks, managing fuel, cleaning soot from glass constantly.
Winding the clockwork that rotated the optic, at intervals through the night.
Cleaning, endlessly, because salt and soot on glass reduce the range.
Keeping records, and in many services operating fog signals, which required running machinery in bad weather.
At isolated stations the shifts were long, the postings were measured in weeks or months, and the accounts written by keepers are consistently about tedium and weather rather than drama.
Why they were automated
Cost, principally. Staffing remote stations is expensive, and the introduction of reliable electric light, automatic bulb changers and remote monitoring removed the need for a person to be present.
Satellite navigation then reduced the importance of the lights themselves, though it did not eliminate it — they remain a backup and a visual reference, and most are still maintained and lit.
The last staffed stations in most countries were automated within the last few decades, which is more recent than people assume.
What the buildings became
Various things, and the variety is interesting.
Accommodation, frequently. Keepers' cottages at automated stations are widely let, and staying in one is a genuinely good way to spend a few days on a coast, with the caveat that they are remote by design.
Museums, at the more accessible ones, often run by volunteers and often very good because the volunteers are frequently former keepers or their families.
Research stations, since a building on a headland with power and access is useful for monitoring weather, birds and marine activity.
And a number are simply sealed and maintained, with the light operating and nobody inside.
Visiting them well
Check whether it is accessible at all, because many are on islands, on rocks, or on private land, and a substantial number can only be seen from a distance or from the water.
The ones with a tower you can climb are worth doing for the optic rather than the view, and the view is usually excellent too.
Ask about the character, meaning the flash pattern, which is published on charts and which the volunteers will happily explain.
And go at dusk if you can, because a lighthouse in daylight is a building and a lighthouse at the moment it becomes visible against a darkening sea is the thing itself.
The other structures on a coast
Lighthouses get the attention and they are part of a wider system worth noticing.
Daymarks are unlit towers and shapes, painted distinctively, serving the same identification function in daylight.
Leading lights are pairs positioned so that when they align vertically from a vessel, it is in a safe channel. Once you know what they are, they are visible at the entrance to most harbours.
Buoys carry their own system of shape, colour and light character indicating which side to pass.
None of this is difficult to learn in outline, and knowing it turns a harbour from scenery into something legible.