Lamps and optics — an overviewLamps and optics — an overview

Lamps and optics – an overview

Lighthouse technology has altered drastically over the centuries. 18th century lighthouses were lit using parabolic mirrors and oil lamps. Documentation

of early examples of parabolic mirrors in the United Kingdom, circa 1760, were documented as consisting of wood and lined with pieces of looking

glass or plates of tin. As described by Searle, “When light hits a shiny surface, it is reflected at an angle equal to that at which it hit. With a light source is placed in the focal point of a parabolic reflector,

the light rays are reflected parallel to one another,

producing a concentrated beam”3.

In 1822, Augustin Fresnel invented the dioptric glass lens. By crafting concentric annular rings with a convex lens, Fresnel had discovered a method

to reduce the amount of light absorbed by a lens. The Dioptric System was adopted quickly with Cordouran Lighthouse (France), fitted with the first dioptric lens in 1823. The majority of heritage-

listed lighthouses in Australia house dioptric lenses made by others such as Chance Brothers (United Kingdom), Henry-LePaute (France), Barbier, Bernard & Turenne (BBT, France) and Svenska Aktiebolaget Gasaccumulator (AGA of Sweden).

These lenses were made in a range of standard sizes, called orders—see Appendix 2. Glossary of lighthouse Terms relevant to Cape Byron Lighthouse.

Early Australian lighthouses were originally fuelled by whale oil and burned in Argand lamps, and multiple wicks were required in order to create a large flame that could be observed from sea. By the 1850s, whale oil had been replaced by colza oil, which was in turn replaced by kerosene, a mineral oil.

In 1900, incandescent burners were introduced. This saw the burning of fuel inside an incandescent mantle which produced a brighter light with less fuel within a smaller volume. Light keepers were required to maintain pressure to the burner by manually pumping a handle as can be seen in Figure 11.

incandescent oil vapour lamp

Figure 11. Incandescent oil vapour lamp by Chance Brothers

dioptric lens

Figure 12. Dioptric lens on display at Narooma