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A lighthouse optic is an assembly of lenses and prisms like the one on the left. It is used to gather as much light from the light source and send it out of the lighthouse in a beam with a characteristic flashing sequence. The photo below shows a panel of an optic. It is roughly circular with a single lens at its centre and is surrounded by complete and broken rings of prisms. The panel is designed to create a single beam of light from the light source. This optic actually has four panels, all similar (the other three cannot be seen) and arranged in a square geometry, so when the optic is rotated it will give out four flashes during the period of rotation. |
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The image at the left approximates to the panel in the photograph. On the left is the front elevation of the panel and on the right is the section through the panel, showing how the lens and prisms draw the light into a beam. For more on this see the later section "How do lenses and prisms work". |
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The image on the left shows a magnificent two-tier optic installed at Hartland Point, Devon, UK in the 1970s. Such an optic had two light sources, one for the upper tier and one for the lower tier. Similar optics were used at Eddystone and Bishop Rock until they were replaced with smaller ones during modernisation programmes. |