Inside Havana lighthouse by Paul Cooklin

Posted by on
Fresnel beehive, made in Paris. A single 220W bulb can be seen 8 miles away using this lens. Early Fresnel lenses were of standard shapes and designs with little deviation such as the one pictured above. They had an oil lantern that burned constantly from dusk until dawn with no flashing or blinking as you may think of them today. Once they started being used along the coasts in greater numbers the mariner could not tell where they were at night because nothing distinguished one light from another. For a lighthouse to be effective as an aid to navigation, it not only had to be seen, it also had to be identified as a unique location. This was necessary if ships were to use it to determine their own location and avoid hazards. From here on out different lenses were made with different characteristics and as such required different lens designs. This meant that a lot of lenses were now unique because they would require flash panels or bull's eyes to distinguish one light from the next. The need to clearly identify each lighthouse was often solved by a specific pattern of flashes per minute. Although sometimes lighthouses identified themselves by using colored light, most made use of a flash of light, followed by a period of darkness. This pattern was called the lighthouse's "characteristic." Once electricity was introduced a light could use a flashing mechanism to give it a unique characteristic flash pattern. Now a sea captain could tell where he was by looking at a map and the flash pattern of the light and tell he was in Maine or Massachusetts... .There are many sizes of Fresnel lenses, called 'orders', the largest being a first order, which is made up of hundreds of glass prisms. The lenses decrease in size through second order, third order, etc. Some have red panels, in order to shine a red light seaward. The glass prisms are shaped and positioned in such a way that the light from the single source inside the lens is reflected outward horizontally through e (Paul Cooklin)

http://bit.ly/bj9L0S
Reactions:

Comments

Post a comment