Whale oil
The light is a third-order Fresnel lens with lenses, prisms and mechanism manufactured in France in 1853. A larger, second-order light had been planned, but delay in shipment caused the present light, originally destined for the Fort Point Lighthouse in San Francisco, to be installed instead. The first light source was a whale oil lantern set inside the lens, whose tank the keeper had to climb the tower to fill several times a night. Whale oil was very expensive and was soon replaced by liquified lard oil which gave way to kerosene in 1880. At the turn of the century, an incandescent vapor lamp was used, followed by electric lights in 1919. From 1912 to 1940 a falling weight mechanism rotated a metal shutter around the light causing the beam to be cut off to seaward for 10 out of every 30 seconds. Thereafter a timed flasher provided the "on/off" characteristic.