Fresnel Lenses

 

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Early lighthouses like the Pharos at Alexandria were lit with open fires.  Whale oil, coiza oil, and lard oil were used until the 1870's when the Lighthouse Service switched to kerosene.  Electricity started to replace kerosene around the turn of the century, and today many lighthouses are solar-powered.  Also, many early lights used wicks until the lens lanterns and parabolic reflectors were introduced.  Then Augustine Fresnel developed a new lens that gathered and focused as much as 85% of the light from the illuminant.  This new invention quickly became the standard in lighthouses first in Europe and then eventually around the world.  Standard Fresnel lenses are classified by size called "orders", with first order being the largest and sixth order the smallest.  There are two non-standard lenses called Hyper-Radial (Makapu'u Point, Hawaii) and Meso-Radial (Abrolhos Island, Brazil & Ilha Rasa, Brazil) which are larger than a first order.  The actual size of the lens is expressed by its inside diameter, and the table below lists the specifications of the seven standard orders of lenses.

Order of Lens Overall height Interior
Diameter
Weight (including metal frame)
Approx.
visibility
Use
1st 7' 10" 72  7/16" 6,000 lbs
22 miles
Coastal lighthouses
2nd 6' 1" 55  1/8" 3,530 lbs
20 miles
Coastal & Great Lakes lighthouses
3rd 4' 8" 39  3/8" 1,985 lbs
18 miles
Coastal & Great Lakes lighthouses
3 1/2 3' 8" 29  1/2" 1,000 to
1,200 lbs
17 miles
made specifically for Great Lakes lighthouses
4th
2' 4"
19  11/16" 440 to 660 lbs
15 miles
mostly for Harbor & River lighthouses
5th 1' 8" 14  3/4" 265 to 440 lbs
10 miles
mostly for Harbor & River lighthouses
6th 1' 5" 11  3/4" 220 lbs
5 miles
mostly for Harbor & River lighthouses

height comparisons of fresnel lenses

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