The original lighthouse produced its light by 21 oil lamps backed by reflectors 54cm in diameter. These were on a three sided rotating base, each side with seven lamps, powered by clockwork. It took six minutes for one rotation, so the lighthouse gave a flash from one of its three sides every two minutes. This light, shone from 60m above the sea level, could be seen up to 30 miles away in the best weather conditions.
Even this light would be of little use in very foggy conditions, so eventually plans were made for a auditory signal, a fog bell. This two-ton bell, installed in 1854, was one of the largest bells in the United Kingdom. It was struck by a clockwork mechanism and was installed on the western tip of the island. After installation the bell proved to be unreliable as a result of salt spray affecting the machinery. A shed was built around it to protect it, but further problems in the design meant that the clockwork needed winding far more often than thought, and would not work at all in poor, windy conditions.

Information taken from www.anglesey-history.co.uk