September–October 2015 57Ma k i ng
light of it
W
HILE THE CRUCIAL function of
lighthouses is unchanged, the
means of delivering their guiding
message has altered radically. In the early 19th
century, the light source was typically groups
of small, oil-burning lanterns backed by
parabolic reflectors. As well as whale and seal
oil, these lanterns – with their large circular
wicks – also used vegetable-based oils, which
were smoky and unreliable.
During the next 100 years, the advent of
pressurised kerosene lights and elaborate
lenses transformed lighthouse technology.
A brilliant invention of French engineer and
physicist Augustin-Jean Fresnel involved a
combination of glass prisms to concentrate
and magnify a light source. First Order lenses- the biggest of these designs – were used in
more than 50 of Australia’s key lighthouses.
Mostly constructed by Chance Bros., a
family company based in Birmingham,
England, these powerful instruments
produced shafts of light reaching more than
40km out to sea. The most potent lighthouse
in Australia is at Cape Byron, on Australia’s
eastern-most point; its light is rated at 2.2
million candela (candela are units of luminous
intensity, and one is approximately equivalent
to the glow of a single candle).
In the early 20th century acetylene-
powered lanterns controlled by ingenious
sun valves were widely used to automate
smaller offshore light beacons.
Meanwhile, electrification and
1000-watt incandescent bulbs
became the standard for our
First Order lighthouses. Over recent
decades it’s the arrival of efficient
LED globes, light sensors and solar
panels that has allowed lighthouse
automation to proceed apace –
thus ensuring a bright future for
our vast and historic network of
night-time beacons.
Bright thinking. The genius of 19th-century
French physicist Augustin-Jean Fresnel is clear in
designs for a Third Order polygonal refl ecting
lens (above). His understanding of optics and
diffraction is revealed in the First Order lens
atop Victoria’s Point Hicks Lighthouse (left) and
the all-conquering loom of Cape Byron’s mighty
Fresnel Lens (below) – Australia’s most powerful.BLUEPRINT: KINGS COLLEGE LONDON / GETTY IMAGES; PHOTOS: AG