“In practice, it was shown not to be necessary to have lights of such great power. In fog or low cloud, light is dissipated by the water vapour in the air so in these kinds of weather conditions it doesn't matter how strong it is, the light just doesn't penetrate over large distances. Putting lighthouses on high cliffs is okay for increasing the visibility, but if the lighthouse was often shrouded in mist and low cloud it rendered them useless.
You might also ask, what is the point of being able to see a light from a distance of fifty miles (80 Km), even if it were possible? There is surely a sensible distance which combines the need to know about a navigational hazard and being too far away for it to matter? So, over time, a balance was struck between the need for a reasonably bright light to be seen at a sensible distance.”