The Lantern

  • Originally , the lantern was a series of reflectors and used whale or seal oil as fuel;
  • In 1908, a 270 degree 4th order Fresnel lens was placed in the lantern room;
  • In 1958, electricity was installed in the lighthouse;
  • A kerosene vapour light was introduced in the late 1950’s, and a weight shaft and pulleys were added, which was set each day.  As the weights fell during the day, the light rotated;
  • The lens was replaced in the late 1950’s with the 4thorder Fresnel Beehive shape lantern with a 700 watt light that was visible for 20 miles (32.2 km);
  • In  2010, the Fresnel Beehive lens was replaced with a low maintenance automatic light triggered by a solar switch.  The present light flashes every 4 seconds and can be seen a distance of about 9 miles;
  • The light was automated in 1985 and a generator installed, making the weight and pulley system obsolete.

The Lantern - 4th Order Beehive Fresnel Lens

The design of the modern lighthouse lens originated at the beginning of the 18th Century. The French inventor Augustin Fresnel (pronounced Frey-nel) had correctly deduced that light was pure energy that traveled in waves, and he then spent his life developing lenses and reflectors that could capture and concentrate light.

The first lighthouse optics that he designed combined highly polished prisms with an array of lenses that captured light and concentrated it back into a main beam. The design was concentric in arrangement, funneling the light into a beam that was many times brighter than its source.  Fresnel’s design of concentric glass rings to concentrate light is still used today in the production of automobile headlights, traffic signals and projectors.

Fresnel produced six sizes of lighthouse lenses, divided into “orders” based on their size and focal length. These are classified as “first” through “sixth” orders. The Panmure Island Lighthouse had a 4th order Fresnel Beehive lens.
Panmure’s rotating Fesnel Lens was replaced with  the present light in 2010. The new lens flashes off and on with a 4 second elipse, has a solar sensor that does not require on-going maintenance and is more energy efficient that the previous light systems. However, the new light can only be seen from 8 nautical miles away where as the light concentrated through the Fresnel lens, could be seen for more than 20 miles away.
Picture
Current lens as of 2010