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What exactly is a Lens-Lantern?

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Postby Zachary » Tue Jun 07, 2005 1:06 pm


I've seen this term in many of my Lighthouse books but I don't know what it is, could someone clarify it for me?
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Postby Lampist » Tue Jun 07, 2005 2:24 pm


Zachary:

I hope to make this one as easy as possible. As you know, in a conventional lighthouse structure you have the lantern at the top of the tower and it "houses" the lens. So the lantern and lens are 2 completely independent structures.

In a lens lantern the 2 components are combined into one structure. Lens lanterns have been around for quite a while so there are many different ones which may add to the confusion.

A buoy lamp is a lens-lantern. The glass or transparent plastic part is the lens while the bronze or aluminum or opaque plastic body of the lamp is the lantern. The beautiful 1 and 8 day oil lamps that were hung on poles as minor aids or on pierhead structures, the cut glass and bronze acetylene aids and even the modern plastic lamps are all lens lanterns. Over the years there have been many sizes of lens lanterns. The smallest one that I know of used in the U. S. was 90 mm, then 150 mm, 200mm, 300 mm, 375 mm and 500 mm. Lightships used the 300, 375 and 500 mm lens-lanterns. The 300 and 375's were also used in the field on AtoN structures but the 500's were pretty much resrved for lightship duty due to their size and weight.

The official definition of a lens lantern from the old Aids to Navigation Manual is "A lantern in which a drum lens is the optic and in which no storm panes are used. The term is practically obsolete". This was in 1953. The term became obsolete because we all suffer from lazy tongues. It is easier to say buoy lamp than lens lantern and it is even easier to say "a 150" or "a 375" because everyone that you work with knows what you are talking about so why use any extra words?

I hope that this information helps.
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Postby Zachary » Tue Jun 07, 2005 2:58 pm


Yes, it does, thanks
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Postby Terry_Pepper » Tue Jun 07, 2005 4:51 pm


Zachary,

Every once in a while you will come across references to 8 or 10-day lens lanterns. Such devices were frequently used on pierhead where they were suspended from the top of a pole.

The photo below shows an 8-day lens lantern. It was so named because the reservoir above the optic itself contained sufficient oil to keep the lamp burning for 8 days without refueling - serving as an early foray into automation.

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Postby Zachary » Tue Jun 07, 2005 7:39 pm


Thank you Terry, these answers sure have helped
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