The light is powered by kerosene. (One night as I was trimmin'
o' the glim' singing a verse from the evenin' hymn) ( which
refers to trimming the wick so that it won't smoke, convex
on a small wick, concave on a large).

The rotation is supplied by weights, like a giant grandfather
clock, which run down the center of the tower.

This is practical, because the entire lens assembly is actually
floated on a trough of mercury, making the frictional losses
nearly nil.

So the keeper's duties amount to making sure the oil reservoir
is filled, that the weights are wound, and the wick is trimmed.
And that the lens is clean.

The light isn't the problem.

Maintaining the keeper is.

Fresh water was brought in, where required, by a supply
vessel. As was food. Kerosene was always brought in.