Hyper-Radial Lenses by Thomas Tag

This document describes hyper-radial or hyper-radiant lenses that are used in lighthouses. It will give you their story from how and why they were created, to how many there were, and where you can see one today.

The idea for lenses of this large size (1330 mm focal length) was mentioned by Thomas Stevenson, Engineer with the Northern Lighthouse Board, in 1869 and first proposed by John Richardson Wigham, Engineer supplying the Commissioners of Irish Lights in 1872, and again proposed by Thomas Stevenson in 1885.

When they were first proposed, they were named Hyper-radiant by Thomas Stevenson. While proposals were made, no lenses were actually produced until 1885 when an extensive trial of lamps, lenses and various fuels was made at the South Foreland Lighthouse in England.  This trial involved representatives from the three English lighthouse authorities, Trinity House covering England and Wales, the Northern Lighthouse Board covering Scotland and the Isle of Man, and the Commissioners of Irish Lights covering Ireland.  In addition many other countries sent representatives to the trials as observers.  It was in 1885 when Chance Brothers Ltd. in England started work toward making this lens size that James Kenward, who directed their Lighthouse Department, renamed this size of lens the Hyper-radial Lens.

The Fresnel Lens

The French Commission for Lighthouses was established on April 29, 1811.  In 1819, Francois Arago, who had become a member of the Commission in 1813, offered to make a systematic review of possible improvements in lighthouse illumination.  He requested that Claude Mathieu and Augustin Fresnel be assigned as his coworkers on the project.  His request was granted on June 21, 1819, and Augustin agreed to serve on the Committee.  Augustin produced his first report on optics and lamps for lighthouses on August 29, 1819, just two months after starting to work on the project.

Augustin designed the first bull's-eye lens panel in early 1821 and a rough test panel was produced by the French optician Francois Soleil later that year. During 1822, Fresnel continued to improve his design for a complete eight sided flashing lens.  He decided that he would need several different sizes of lenses for various lighthouse types and he started with five sizes, which he named orders.

ORDER                              FOCAL LENGTH

First                                      920mm

Second                                  700mm

Third Large                           500mm

Third Small                           375mm

Fourth                                   250mm

The order was determined by measuring from the center of the lens at the focus to the inside surface of each lens panel.  Shortly after his first designs, Augustin added fifth and sixth order lens sizes, and many years later still other lens orders were added.  I will not go into all of these other sizes because this story is about the Hyper-radial lens and how it came to be developed.  Suffice it to say that the Hyper-radial lens has a focal length of 1330mm and is therefore significantly larger than the first order lens.

The Need for Larger Lenses

When Augustin Fresnel first deployed his lens in 1823 at the Cordouan Lighthouse in France, the largest lamp, which had been designed by Fresnel and his mentor Francois Arago, consisted of just 4 concentric wicks burning Colza Oil.  However, by the late 1860s many new lamps were being designed and the lamp fuel was about to switch to the more powerful kerosene and coal gas.

Thomas Stevenson took note of these impending changes and suggested that with lamps of 5, 6 and 7 concentric wicks and powerful kerosene and gas for fuels, the flame in a 1st order lens would become ex-focal and much of the increased light would be lost.  Thomas therefore suggested, late in 1869, that larger lenses would be required in the future, although he took no action to propose a specific size or to have a test lens made.  In his suggestion he named these larger lenses "Hyper-radiant" due to their increased power.

In Ireland, John Wigham had produced his first small "Crocus" gas burner in 1863 and had continuously improved the design producing his huge "Composite" gas lamp in late 1868. Wigham thought that gas was a better fuel and that he could produce a lamp that could easily be increased in power by the keeper during times of fog.  The Composite burner allowed the keeper to start with 28 gas jets and to increase their number to 48, 68, 88 and finally 108 jets.

Wigham's Composite 108-Jet Gas Burner

In 1872, John Wigham proposed that a Hyper-radiant lens be constructed in a paper he presented to the Royal Dublin Society; however, no further action was taken.  By 1877, Wigham's huge gas powered lamp was in use in 1st order lenses and the flame was so large that much light was ex-focal and lost.  In an attempt to solve the problem, John went to the French firm of F. Barbier and asked them to design a new larger lens and to provide him with design drawings and a cost estimate.  He received the drawings for a lens with a 1330mm focal length, but he did not have the political power to get permission to have the lens produced.

The Lighthouse Lamp Burners of 1884-85

By 1884, further significant progress had been made in the development of much larger lamp burners.  In England, James Douglass was in the process of creating 7-wick and a 10-wick, kerosene lamps (although the largest lamp then in actual use was a 6-wick) and was in the process of developing a 10-ring gas burner.  In Ireland, John Wigham had perfected his 108-jet gas burner whose flame was over eleven inches in diameter and he also was working on a 10-ring gas burner although he was sure that the 108-jet burner was all that would be needed.

Douglass 10-wick Burner

Wigham's 10-ring Gas Burner

These large lamps were becoming a concern to the lens makers. Chance Brothers, Sautter and Henry-Lepaute were concerned that the great heat produced by these lamps could damage the 1st order lenses in which they were used and some actual cracking of prisms had occasionally been seen.  

At the same time, there was a great debate about the use of electricity and coal gas, and all of the lighthouse authorities were questioning which fuel was the safest, produced the brightest light and was the easiest to use.  In an effort to resolve these questions it was decided that an extensive trial would be held at the South Foreland Lighthouse in southeastern England.  

The Great Trials of 1884-85

These trials were set up to test the use of electricity, gas, and kerosene as fuels.  At the same time various new and larger lamps were tested and the latest lenses that were arranged one above the other were tried.

There were three test towers set up near the lighthouse at South Foreland England. These test towers could be observed from several points on land as well as from the sea.  In addition a large photometric building was erected to allow the detailed examination of the candlepower of each style of lamp and fuel.

The first test tower was designated for electricity and had one Fresnel lens.  The second tower was for testing gas and had four lenses one above the other in what was known as a quadriform lens.  There were also four of Wigham's 108-jet gas burners mounted one above the other with one to each lens. The third tower was for testing kerosene and had three lenses one above the other in a triform arrangement with three six-wick oil lamps arranged one above the other with one to each lens.

During the planning for the trials David A. Stevenson and his partner Charles A. Stevenson who were engineers for the Northern Lighthouse Board in Scotland, discussed the large diameter lamp flames with their brother Thomas Stevenson and all decided that a larger lens with a greater focal distance should be tested as a part of the trials.  David and Charles contacted the F. Barbier Company, in France, and requested that a larger lens panel be produced.  F. Barbier responded with the design they had previously proposed to John Wigham of 1330 mm focal distance.  It was also decided to compare this new 1330 mm panel with the largest lens panel then in existence, which was the extra-tall first-order 920mm panel for the Eddystone Lighthouse. 

Drawing Showing the Hyper-radiant 1330mm Lens and 920mm Eddystone Lens

 

During the trials there was great interest in the new lens panels and in what the results of using this larger lens size would be.  It was found that Wigham's large gas burners did crack one of the standard first order lenses and that the massive flame did become ex-focal with a corresponding loss of light.  When Wigham's burner was used with the Hyper-radiant lens panel no damage occurred and there was a significant increase in light output.

When James Kenward of Chance Brothers saw the new lens panel he was greatly impressed.  However, he did not like the name Hyper-radiant and proposed the name Hyper-radial, which was accepted and remains the most common name in use for these lenses today.     

There were many results of the trials and much controversy as to the results.  Some observers suggested that the trials were comparing "apples and oranges" and "current technology with proposed technology," but the results were generally accepted. Electricity should only be used in the critical coast lights, kerosene was generally as good as or better than gas, and the new Hyper-radial panels should be used with large kerosene burners and with gas if gas were to be used.

So Where Were These Lenses and Where are they Now?

The best currently available information suggests that there were a total of 31 individual lighthouses where Hyper-radial Lenses were installed.  There are supposed to be 4 currently in museums, 12 still in their towers, 5 removed from their towers with their current location unknown, 6 definitely destroyed, and 6 in storage.  This adds to 33, but the Bishop Rock Lens was split and one-half is still in the tower and one-half is in storage and the Bazaruto Island lens is in the tower, but mostly destroyed.  The chart below shows their locations.

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Styles of Hyper-radial Lenses

There were three styles of Hyper-radial lenses produced.  The first design used prism panels that were designed in the same style as all other Fresnel Lenses - just larger.  This style was the major one used for Hyper-radial Lenses. However, a Hyper-radial lens made with the standard design was very tall and required a lantern that was both dramatically larger in diameter as well as in height. Charles Stevenson, Engineer of the Northern Lighthouse Board in Scotland, thought that he could develop a better design.

In 1891, Charles invented what he called the Spherical Lens Design.  In the Spherical Design the lens panel was shaped with the center bull's-eye lens set at 1330mm from the focus and with each succeeding prism ring placed further away from the focus (see drawing).  This worked well as long as the light reaching the outermost prism did not have an angle of more than 40 degrees. Charles first tried this design at the Fair Isle North Lighthouse in Scotland in 1892.

Charles was not finished and he then designed the Equiangular Prism Lens, where the central portion of the lens was made with the bull's-eye at 1330mm from the focus and each succeeding prism ring placed closer to the focus until the light reaching the outermost prism had an angle of about 20 degrees, then the succeeding prisms were again placed farther from the focus (see drawing). This design was first used at the Sule Skerry Lighthouse in Scotland in 1895.

The Equiangular Design provided still greater efficiency in the area where the light had to be bent from 30 to 40 degrees.  Unfortunately, the equiangular prisms were very difficult to produce and therefore expensive thus this design was seldom used.  However, both of Charles' designs allowed for smaller and less costly lanterns.

Standard, Spherical and Equiangular Lens Designs

The Lens at Berlengas Island, Portugal

The lens at Berlengas Island Portugal was built by the Barbier & Benard Company in France in 1897.  It had three bull's-eye panels covering 60 degrees each.  It was removed in 1985 and the three panels are located as follows: one is in the Directorate of Lighthouses Museum in Paco de Arcos a part of Lisbon, a second panel is in the Santa Marta Lighthouse Museum in Lisbon, and the third panel is slightly damaged and is in storage at the Directorate of Lighthouses facility in Lisbon.

Barbier & Benard Photo

Lens Panel in the Directorate of Lighthouses Museum

 

The Lens at the Bishop Rock, England

The lens at Bishop Rock, England was built by the Chance Brothers Company in England in 1887.  It was a two level bi-form lens where each level had five bull's-eye panels covering 72 degrees each.  The upper lens was removed in 1992 and the five panels of the upper lens were originally shown at the Trinity House Museum in Penzance.

Bishop Rock Lens Drawing by Chance Brothers

 

Bishop Rock Upper Lens

The Lens at Cabo de Sao Vicente, Portugal

The lens at Cabo de Sao Vicente, Portugal was built by the Barbier & Benard Company in France in 1906.  It has three bull's-eye panels covering 120 degrees each. It was placed in operation in 1908 and is still in operation in the tower.

Cabo de Sao Vicente Lens Photo by Barbier & Benard

The Lens at Cap d'Antifer, France

The lens at Cap d'Antifer, France was built by the F. Barbier Company in France in 1889.  It had six bull's-eye panels covering 60 degrees each. It was placed in operation in 1894 and was destroyed by German troops on August 29, 1944.

Cap d'Antifer Lens Drawing by F. Barbier

Cap d'Antifer Photo by F. Barbier

The Lens at Cape Race, Newfoundland - Canada

The lens at Cape Race, Canada was built by the Chance Brothers Company in England.  It has four bull's-eye panels covering 90 degrees each.  The lens was installed in 1907.  The lens is currently functional in the tower. 

Cape Race Lens Drawing by Chance Brothers

Cape Race Photo by Chance Brothers

The Lens at Kinnaird Head, Scotland

The lens at Kinnaird Head, Scotland was built by the Chance Brothers Company in England.  It is a combination Hyper-radial and First order lens.  It has two bull's-eye Hyper-radial panels and four partial bi-valve first order panels formed into two bi-valve sides covering 180 degrees each.  This lens uses the Equiangular Prism Design of Charles Stevenson for the Hyper-radial panels.  The lens was installed in 1902.  The lens is currently functional in the tower, which is a part of the Museum of Scottish Lighthouses.

Kinnaird Head Drawing by Chance Brothers

Photo of the Inside of the Kinnaird Head Lens

The Lens at Makapu'u Point, United States

The lens at Makapu'u Point, Hawaii USA was built by the Barbier & Benard Company in France in 1887.  This was the first complete Hyper-radial lens ever built and the only example of a fixed Hyper-radial lens.  It is a fixed lens with panels covering 360 degrees.   It was originally designed for Mosquito Inlet, Florida (now Ponce Inlet), but was never sent there. Instead, it was shown by the Lighthouse Establishment at many fairs and expositions.  It was installed at Makapu'u Point in 1909 and is still functional in the tower.

Makapu'u Point Lens Photo by Barbier and Benard

Makapu'u Point Lens Photo by USCG

The Lens at Manora Point, Pakistan

The lens at Manora Point, Pakistan was built by the Chance Brothers Company in England.  It has four bull's-eye panels covering 90 degrees each.  The lens was installed in 1908.  The lens is currently functional in the tower. 

Drawing of Manora Point Lens by Chance Brothers

Photo of Manora Point Lens by Chance Brothers

The Lens at the Bell Rock, Scotland

The Lens at the Bell Rock, Scotland was built by the Henry-Lepaute Company in France in 1901.  This is the only known Hyper-radial Lens to have been built by Henry-Lepaute.  It was the largest Fresnel lens to be placed in the Bell Rock Lighthouse tower where it was installed in 1902.  The lens was a composite of a Hyper-radial and a first order.  It had a Hyper-radial panel using the equiangular prism design and two partial first order panels covering 180 degrees and formed into one half of a bi-valve lens configuration.  This side of the lens used both interior and exterior red panels to produce a red flash.  The opposite side of the lens consisted of two first-order 90-degree totally-reflecting prism panels to further increase the light to the red side of the lens.  In the center of the totally reflecting prism panels was a single Hyper-radial flash panel of the spherical design that projected a white light, in the opposite direction from the red side, and at each edge of this side of the lens were small vertical prism lenses that also projected white light in this direction.  Thus one side of the lens produced a very strong red flashing light and the opposite side of the lens produced a white flashing light of equal power.

This lens was removed from the tower in 1964.  One half of one of the Hyper-radial panels can be seen at the Signal Tower Museum in Arbroath, Scotland.  The location of the remainder of the lens is unknown.

Drawing of the Composite Red and White Lens at Bell Rock by Henry-Lepaute

The Lens at Fair Isle North, Scotland

The lens at Fair Isle North, Scotland was built by the F. Barbier Company in France in 1892.  It was a four sided double flashing lens having four panels each covering 90 degrees and using the Spherical Prism Design for the central portion and the Equiangular Prism Design for the edges.  It was installed at Fair Isle North in 1892 and was later removed from Fair Isle North on April 23, 1980 and its current status is unknown and possibly destroyed.

Drawing of the Lens at Fair Isle North by F. Barbier

Photo of the Lens at Fair Isle North by F. Barbier

The Lens at Bazaruto Island, Mozambique

The lens at Bazaruto Island, Mozambique was built by the Barbier & Benard Company in France in 1913.  It was a flashing lens with three panels each covering 60 degrees and a 180-degree totally reflecting prism panel in the rear.  It was installed at Bazaruto Island in 1913 where it remains in the tower mostly destroyed and replaced by a small rotating lens mounted inside.

Photo of the Bazaruto Island Lens (c) Sam Seyffert and used with permission

The Lens at Round Island, England

The lens at Round Island, England was built by the Chance Brothers Company in England in 1888.  It was a two level bi-form lens where each level had six bull's-eye panels covering 60 degrees each.  This lens displayed a flashing red light.  The lens was removed in 1966 and its location is unknown.

Drawing of the Lens at Round Island by Chance Brothers

Photo of the Round Island Lens by Chance Brothers

The Lens at Hyskeir Island, Scotland

The lens at Hyskeir, Scotland was built by the Chance Brothers Company in England.  It had three bull's-eye panels covering 60 degrees each.  These panels are another example of the use of the Spherical Panel design.  Behind the Bull's-eye panels was a 180-degree totally reflecting prism panel, which intensified the light to the bull's-eye panels. The lens was installed in 1904.  The lens is currently operational in the tower.

The Hyskeir Lens from the Front (c) Patrick Tubby

The Hyskeir Lens from the Rear (c) Patrick Tubby

The Original Lens at Tory Island, Ireland

The original lens at Tory Island, Ireland was built by the F. Barbier Company in France in 1887.  It was a tri-form flashing lens (three lenses one above the other) with each lens having six panels each covering 60 degrees.  It was installed at Tory Island in 1887 and was later removed from Tory Island in 1928 and reduced to a bi-form configuration and re-installed at Mew Island where it was removed in August 2014 to be displayed in Belfast.

Drawing of the Original Tower and Lens at Tory Island by F. Barbier

The Current Lens at Tory Island, Ireland

The current lens at Tory Island, Ireland was built by the Chance Brothers Company in England in 1928.  It is a bi-form flashing lens (two lenses one above the other) with each lens having four lens panels each covering 60 degrees and two blank metal panels that were used to produce a 4 group flashing characteristic.  It was installed at Tory Island in 1928 where it remains in the tower and functional.

Photo of the Tory Island Lens by Chance Brothers

The Lens at Sule Skerry, Scotland

The lens at Sule Skerry, Scotland was built by the Barbier & Benard Company in France.  It has three triple group-flashing bull's-eye Hyper-radial panels covering 120 degrees each.  This lens uses the Equiangular Prism Design of Charles Stevenson for the Hyper-radial panels. The lens was installed in 1895.  The lens was removed from the tower in April 1977 and its current location is in storage at the National Museum of Scotland.

Photo of the Sule Skerry Lens by Barbier & Benard (c) National Museum of Scotland From the book: "Northern Lights" by Dr. A. D. Morrison-Low, Used with Permission

The Lens at Rubh' Re, Scotland

The lens at Rubh' Re, Scotland was built by the Chance Brothers Company in England.  It has six bull's-eye panels covering 30 degrees each.  These panels are another example of the use of the Spherical Panel design.  Behind the Bull's-eye panels is a 180-degree totally reflecting prism panel, which intensified the light to the bull's-eye panels. The lens was installed in 1909. The lens was removed from the tower in 1985 and was sent to the Gairloch Heritage Museum where it is currently on display.

Photo of the Back of the Rubh' Re Lens (in the Foreground) by Chance Brothers
 

Drawing of Rubh' Re Lens Light Pattern

Photo of Rubh' Re Lens in Gairloch Museum

The Lens at Pladda, Scotland

The lens at Pladda, Scotland was built by the Chance Brothers Company in England.  It had three bull's-eye panels covering 60 degrees each.  These panels are our first example of the use of the Spherical Panel design.  Behind the Bull's-eye panels was a 180-degree totally reflecting prism panel, which intensified the light to the bull's-eye panels. The lens was installed in 1901.  The lens is not in the tower.  It was reportedly sent to the Arran Heritage Museum on the Isle of Arran, but they state that it is not there. 

Photo of the Front of the Pladda Lens by Chance Brothers

Photo of the Side of the Pladda Lens by Chance Brothers

Drawing of the Plan View of the Front of the Pladda Lens by Chance Brothers

The Lens at Pei-Yu-Shan, China

The lens at Pei-Yu-Shan, China (sometimes known as Beiyushan) was built by the Barbier & Benard Company in France.  It is a flashing lens with 4 panels, each covering 90 degrees.   Each lens panel has two partial bull's-eyes giving a double group-flashing characteristic.   It was installed at Pei-Yu-Shan, China in 1895.  It is not in the tower and its current location is unknown.

Photo of the Tower and Lens at Pei-Yu-Shan, China by Barbier, Benard and Turenne

Photo of the Inside of the Pei-Yu-Shan Lens

The Lens at Pakri (Pakerort), Estonia

The lens at Pakri (Pakerort), Estonia was built by the F. Barbier Company in France. It is a fixed lens covering 240 degrees.  It also has two outer vertical prism sections that produce a flashing light in two directions.  One flash panel covers 30 degrees while the other covers 80 degrees.  It also has a totally reflecting prism panel that reinforces the light in the main direction.  This lens was installed at Pakri, in 1889. The lens is not in the tower and was destroyed in 1941 early in WWII.

Drawing of the Lens at Pakri, Estonia by F. Barbier

Photo of the Lens at Pakri, Estonia by F. Barbier

The Lenses at Orford Ness, England

The lenses at Orford Ness, England were built by the Chance Brothers Company in England. These are called subsidiary lenses because they are positioned low in the tower well below the main lens, which is a second order.  These subsidiary lenses light specific sectors of the sea to guide ships as they approach the lighthouse.  There are two fixed lens panels each covering 30 degrees and pointing in two separate directions.  There also are two totally reflecting prism panels, one for each of the hyper-radial panels.  The lenses were installed in 1909.  The lenses were removed in 2014 and are in storage. 

Photo of the Orford Ness Subsidiary Lenses (c) by Juergen Tronicke

The Lens at Nólsoy, Faroe Islands

The lens at Nólsoy, Faroe Islands was built by the F. Barbier Company in France.    It is a flashing lens with twelve panels each covering 30 degrees.    It was installed at Nólsoy, in 1893 and is still in the tower and functional.

Photo of the Lens at Nólsoy, Faroe Islands (c) by Nigel Homer

The Lens at Mew Island, Ireland

The lens at Mew Island, Ireland was built by the F. Barbier Company in France in 1887.  It is a bi-form flashing lens (one lens above the other) with each lens having four panels each covering 60 degrees and two blank metal panels that were used to produce a 4 group flashing characteristic.   It was originally designed for Tory Island, Ireland, as a tri-form lens (three lenses one above the other). It was installed at Tory Island in 1887 and was later removed from Tory Island in 1928 and reduced to a bi-form configuration and re-installed at Mew Island where it remained until August 2014. It is now located at the Ticanic Foundation in Belfast Ireland where it is on display.

Drawing of the Mew Island Lens by F. Barbier 

Mew Island Lens Photo by F. Barbier Company.

THE LENS AT SPURN POINT, ENGLAND

The lens at Spurn Point, England was built by the Chance Brothers Company in England in 1895.  It was a flashing lens with six bull's-eye panels covering 60 degrees each.  This lens displayed a flashing white light.  The lens was removed in 1986 and its location is unknown.

Photo of the lens for Spurn Point England by Chance Brothers

THE LENS AT Buchan Ness, SCOTLAND

The lens at Buchan Ness, Scotland was built by the Chance Brothers Company in England.  It is a combination Hyper-radial and First order lens.  It has two bull's-eye Hyper-radial panels and other first order panels formed into two bi-valve sides covering 180 degrees each.  The lens was installed in 1910.  The lens was removed in 1978 and is currently in storage at the Museum of Scottish Lighthouses.

Photo of the lens for Buchan Ness Scotland by Chance Brothers - Photo courtesy Museum of Scottish Lighthouses

THE LENS AT FLANNAN ISLANDS, SCOTLAND

The lens at Flannan Islands, Scotland was built by the Henry-Lepaute Company in France in 1899.  It was a two sided double flashing bi-valve style lens having two panels each covering 180 degrees and using Equiangular Prism Design for the edges.  It was installed at Flannan Islands in 1899 and was later removed from Flannan Islands in 1971 and was destroyed by the Northern Lighthouse Board personnel.

Photo of the lens for Flannan Islands Scotland by Henry-Lepaute - Photo courtesy Museum of Scottish Lighthouses