Existing comment:
The glass prisms of the Fresnel lens bent light into a concentrated beam. With one lamp in the center of the lens, it was possible to send out a horizontal beam of light of 360 degrees.
At first Fresnel lenses were used with an Argand-type lamp. These lamps were modified over the years by developing various ways to deliver fuel to the wick.
The last type of oil lamp used in the Bay's lighthouses was the mantle type, similar to today's Coleman lanterns. These lamps were known as the "incandescent oil vapor type" and used kerosene for fuel.
The adoption of electricity in the 1930s changed the lighthouse and the lives of its keepers dramatically. Used with the Fresnel lens, the electric bulb produced no suit so little cleaning was required. It was dependable, and could be put on an automatic timer.
The electrical bulb and Fresnel lens system is still used in some Bay lighthouses; however, powerful aero-beacon type bulbs are replacing the Fresnel lenses on new installations. |