Lighthouse lights rotate constantly for maximum visibility of the lights.
If the lights were to just shine in one location it could cause blinding for the people that are on the ocean and approaching the lighthouse.
The shining light also indicates not just a light but since the light is rotating it indicates that there is a lighthouse there instead of it just sitting there shining.
That shows the people that there is something up ahead that they need to watch for in the night so they don't crash the boat or other vessel into it.
The lighthouses that remain today are mostly automated and have no keepers in them to operate the lighthouse.
More useful electronic navigation systems have also made lighthouses almost obsolete but some lighthouses to remain in use today.
But those lighthouses are automated without need for much human intervention like they would need in the old days before all the technology of today.
The UK’s last lighthouse custodian left his post at the North Foreland Lighthouse in Kent in 1998 – the same year, the US Coast Guard automated the last of its 279 federally run beacons. Australia, Finland, Iceland, Ireland, Japan, New Zealand, Norway and many other nations no longer employ a single operator.
One stalwart sentinel remains in South Africa; three in France; a handful in India, Myanmar (also known as Burma) and Portugal; and fewer than 50 in Canada.